1. Fire Bird V ATMEGA2560
NEX Robotics
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Fire Bird V Software Manual
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NEX Robotics
Fire Bird V Software Manual
FIRE BIRD V
SOFTWARE MANUAL
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NEX Robotics
Fire Bird V Software Manual
Version 2.00
December 3, 2010
Documentation author
Sachitanand Malewar, NEX Robotics Pvt. Ltd.
Anant Malewar, NEX Robotics Pvt. Ltd. and M. Tech, IIT Bombay
Credits (Alphabetically)
Aditya Sharma, NEX Robotics
Amey Apte, NEX Robotics
Anant Malewar, EE, M.Tech, IIT Bombay
Ashish Gudhe, CSE, M.Tech, IIT Bombay
Behlul Sutarwala, NEX Robotics
Gaurav Lohar, NEX Robotics
Gurulingesh R. CSE, M.Tech, IIT Bombay
Inderpreet Arora, EE, M.Tech, IIT Bombay
Prof. Kavi Arya, CSE, IIT Bombay
Prof. Krithi Ramamritham, CSE, IIT Bombay
Kunal Joshi, NEX Robotics
Nandan Salunke, RA, CSE, IIT Bombay
Pratim Patil, NEX Robotics
Preeti Malik, RA, CSE, IIT Bombay
Prakhar Goyal, CSE, M.Tech, IIT Bombay
Raviraj Bhatane, RA, CSE, IIT Bombay
Rohit Chauhan, NEX Robotics
Rajanikant Sawant, NEX Robotics
Saurabh Bengali, RA, CSE, IIT Bombay
Vaibhav Daghe, RA, CSE, IIT Bombay
Vibhooti Verma, CSE, M.Tech, IIT Bombay
Vinod Desai, NEX Robotics
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Notice
The contents of this manual are subject to change without notice. All efforts have been made to
ensure the accuracy of contents in this manual. However, should any errors be detected, NEX
Robotics welcomes your corrections. You can send us your queries / suggestions at
[email protected]
Content of this manual is released under the Creative Commence cc by-nc-sa license. For legal
information refer to: http://creativecommons.org/licenses/by-nc-sa/3.0/legalcode
Robot’s electronics is static sensitive. Use robot in static free environment.
Read the hardware and software manual completely before start using this
robot
Recycling:
Almost all of the robot parts are recyclable. Please send the robot parts to the recycling plant
after its operational life. By recycling we can contribute to cleaner and healthier environment for
the future generations.
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Important:
1. User must go through the Fire Bird V’s Hardware and Software manuals
before using the robot.
2. Crystal of the ATMEGA2560 microcontroller is upgraded to 14.7456MHz
from 11.0592 MHz in all the Fire Bird V ATMEGA2560 robots delivered on
or after 1st December 2010. This documentation is made considering crystal
frequency as 14.7456MHz.
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Index
1.
Fire Bird V ATMEGA2560
7
2.
Programming the Fire Bird V ATMEGA2560 Robot
11
3.
Input / Output Operations On the Robot
46
4.
Robot Position Control Using Interrupts
64
5.
Timer / Counter Operations On The Robot
74
6.
LCD Interfacing
89
7.
Analog to Digital Conversion
95
8.
Serial Communication
103
9.
SPI Communication
111
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1. Fire Bird V ATMEGA2560
The Fire Bird V robot is the 5th in the Fire Bird series of robots. First two versions of the robots
were designed for the Embedded Real-Time Systems Lab, Department of Computer Science and
Engineering, IIT Bombay. Theses platforms were made commercially available form the version
3 onwards. All the Fire Bird V series robots share the same main board and other accessories.
Different family of microcontrollers can be added by simply changing top microcontroller
adaptor board. Fire Bird V supports ATMEGA2560 (AVR), P89V51RD2 (8051) and LPC2148
(ARM7) microcontroller adaptor boards. This modularity in changing the microcontroller
adaptor boards makes Fire Bird V robots very versatile. User can also add his own custom
designed microcontroller adaptor board.
Fire Bird V ATMEGA2560 (AVR)
Fire Bird V P89V51RD2 (8051)
Fire Bird V LPC2148 (ARM7 TDMI)
Figure 1.1: Fire Bird V Robots
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Figure 1.2: ATMEGA2560 (AVR), P89V51RD2 (8051) and LPC2148 ARM7
microcontroller adaptor boards for Fire Bird V
1.1 Avatars of Fire Bird V Robot
All Robots use the same main board and microcontroller adaptor board. All Fire Bird V Robots
share the same unified architecture.
Fire Bird V
Fire Bird V Insect
Fire Bird V Tank
Fire Bird V Hexapod
Fire Bird V Omnidirectional Robot
Fire Bird V 4WD with Gripper
Figure 1.3: Avatars of Fire Bird V Robot
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Figure 1.4 Fire Bird V ATMEGA2560 robot
2.2 Fire Bird V Block Diagram:
Figure 1.5: Fire Bird V ATMEGA2560 robot block diagram
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1.3 Fire Bird V ATMEGA2560 technical specification
Microcontroller:
Atmel ATMEGA2560 as Master microcontroller (AVR architecture based Microcontroller)
Atmel ATMEGA8 as Slave microcontroller (AVR architecture based Microcontroller)
Sensors:
Three white line sensors (extendable to 7)
Five Sharp GP2D12 IR range sensor (One in default configuration)
Eight analog IR proximity sensors
Eight analog directional light intensity sensors
Two position encoders (extendable to four)
Battery voltage sensing
Current Sensing (Optional)
Indicators:
2 x 16 Characters LCD
Indicator LEDs
Buzzer
Control:
Autonomous Control
PC as Master and Robot as Slave in wired or wireless mode
Communication:
Wireless ZigBee Communication (2.4GHZ) (if XBee wireless module is installed)
USB Communication
Wired RS232 (serial) communication
Simplex infrared communication (From infrared remote to robot)
Dimensions:
Diameter: 16cm
Height: 10cm
Weight: 1300gms
Power:
9.6V, 2100mAh Nickel Metal Hydride (NiMH) battery pack and external Auxiliary power from
battery charger.
Battery Life:
2 Hours while motors are operational at 75% of time
Locomotion:
Two DC geared motors in differential drive configuration and caster wheel at front as support
• Top Speed: 24 cm / second
• Wheel Diameter: 51mm
• Position encoder: 30 pulses per revolution
• Position encoder resolution: 5.44 mm
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2. Programming the Fire Bird V ATMEGA2560 Robot
There are number of IDEs (Integrated Development Environment) available for the AVR
microcontrollers. There are free IDEs which are based on AVR GCC like AVR Studio from
ATMEL and WIN AVR and proprietary IDEs like ICC AVR, Code vision AVR, IAR and KEIL
etc. IDEs like ICC AVR and code vision AVR are very simple to use because of their GUI based
code generator which gives you generated code. Almost all the proprietary IDEs works as full
version for first 45 days and then there code size is restricted to some size. We have used AVR
Studio from ATMEL which is feature rich free to IDE for the robot. In this manual we are going
to focus on the AVR studio from the ATMEL. It uses WIN AVR open source C compiler at the
back end. It has many attractive features like built-in In-Circuit Emulator and AVR instruction
set simulator. After writing and compiling the program it gives “.hex” file. This “.hex” file needs
to be loaded on the robot using In System Programmer (ISP).
IDE Installation
Since AVR studio uses WIN AVR compiler at the back end we need to install WIN AVR first
before installing AVR studio. By doing so AVR Studio can easily detect the AVRGCC plug-ins.
2.1 Installing WIN AVR
Copy “WIN AVR 2009-03-13” from the “Software and Drivers” folder of the documentation CD
on the PC and click on WinAVRxxxx.exe file.
Figure 2.1
The following window with WIN AVR installation package will open. Choose language as
“English”.
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Figure 2.2
Click next in the WIN AVR setup wizard.
Figure 2.3
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Press “I Agree” after going through license agreement.
Figure 2.4
Make sure that you have to select the drive on which operating system is installed.
Figure 2.5
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Select all the components and press “Install”.
Figure 2.6
Click “Finish” to complete WIN AVR installation
Figure 2.7
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2.2 Installing AVR Studio
Go to “Software and Drivers” folder from the documentation CD, copy folder “AVR Studio
4.17” on the PC and click on “AvrStudio417Setup.exe” to start the installation process.
Figure 2.8
Click on “Run”
Figure 2.9
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Click “Next” to start installation of AVR Studio 4
Figure 2.10
After clicking “Next”, go through the license agreement. If it is acceptable then click “Next”
Figure 2.11
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Now choose the destination drive. Select the same drive in which your operating system and
WINAVR is installed.
Figure 2.12
Select for the “Install / upgrade Jungo USB Driver” to support In System Programming (ISP) by
AVRISP mkII
Figure 2.13
Important: If “Install / upgrade Jungo USB Driver” is not selected then AVRISP mkII
programmer will not work with the AVR Studio.
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Click “Next” to start the installation process.
Figure 2.14
Click “Finish” to complete the installation process.
Figure 2.15
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2.3 Setting up Project in AVR Studio
AVR studio is an Integrated Development Environment (IDE) for writing and debugging AVR
applications. As a code writing environment, it supports includes AVR Assembler and any
external AVR GCC compiler in a complete IDE environment.
AVR Studio gives two main advantages:
1. Edit and debug in the same application window. Faster error tracking.
2. Breakpoints are saved and restored between sessions, even if codes are edited.
Figure 2.16
Middle window shows current code under development. Window on the left side shows view of
source files, header files, External dependencies, and other files. Right side window shows all the
ports and other peripheral’s status. Bottom window is known as Build window. It shows results
of the compilation, errors, HEX file size and other warning messages etc.
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1. Open AVR Studio. If any project is running it can be closed by clicking on Project in the
menu bar and select Close Project.
2. To create a new project, click on Project in the menu bar and select “New Project”.
Figure 2.17
3. Select Project Type as “AVR GCC”. Type project name in the “Project name” window. In this
case it is “buzzer_test”. Also check on Create initial file and Create folder check box. This will
create all the files inside the new folder. In the Location window select the place where would
like to store your project folder and then click “Next”.
Figure 2.18
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4. Select debug platform and Device. In this case we have selected “AVR simulator” and
“ATMEGA2560” microcontroller and click finish.
Figure 2.19
5. Now we are almost ready to write our first code. Before we start coding we will check other
setting to make sure that they are set properly.
Figure 2.20
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6. Open Project menu and click on the Configuration option.
Figure 2.21
7. In the Project Option “General” tab will open. Select device as “ATMEGA2560” and
frequency (Crystal Frequency) as 14.7456MHz i.e. 14745600Hz. Set the optimization level be at
“-O0”.
Figure 2.22
Selecting proper optimization options
“Optimization” option defines the optimization level for all files. Higher optimization levels will
produce code that is harder to debug. Stack variables may change location, or be optimized
away, and source level debugging may "skip" statements because they too have been optimized
away.
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The levels of optimization are:
• -O0 No optimization. This is the same as not specifying any optimization.
• -01 Optimize. Reduces code size and execution time without performing any
optimizations that take a great deal of compilation time.
• -O2 Optimize even more. avr-gcc performs almost all optimizations that don't involve a
space-time tradeoff.
• -O3 Optimize yet more. This level performs all optimizations at -O2 along with -finlinefunctions and -frename-registers.
• -Os Optimize for size. Enables all -O2 optimizations that don't increase code size. It also
performs further optimizations designed to reduce code size.
For more information on optimization, see the 'man' pages for avr-gcc.
Important: During the coding choose appropriate optimization option. If you feel that code is
not working properly as it should be then turn off all optimization by selecting optimization
option as “-O0”. Once you know that your code is properly working then you can incrementally
increase optimization level.
We suggest that always use optimization level as “-O0” at the beginner level.
8. Make sure that in the External Tools, proper path for avr-gcc.exe and make.exe are given and
press ok.
Now we are ready to write our first code.
Figure 2.23
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2.4 Writing your first code in AVR Studio
This program will make robot’s buzzer beep.
Copy the following code in window “code area” as shown in figure 2.25. We will see how this
code works in the next chapter.
//Buzzer is connected at the third pin of the PORTC
//To turn it on make PORTC 3rd (PC3 )pin logic 1
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
//Function to initialize Buzzer
void buzzer_pin_config (void)
{
DDRC = DDRC | 0x08;
//Setting PORTC 3 as output
PORTC = PORTC & 0xF7; //Setting PORTC 3 logic low to turnoff buzzer
}
void port_init (void)
{
buzzer_pin_config();
}
void buzzer_on (void)
{
unsigned char port_restore = 0;
port_restore = PINC;
port_restore = port_restore | 0x08;
PORTC = port_restore;
}
void buzzer_off (void)
{
unsigned char port_restore = 0;
port_restore = PINC;
port_restore = port_restore & 0xF7;
PORTC = port_restore;
}
void init_devices (void)
{
cli();
//Clears the global interrupts
port_init();
sei();
//Enables the global interrupts
}
//Main Function
int main(void)
{
init_devices();
while(1)
{
buzzer_on();
_delay_ms(1000); //delay
buzzer_off();
_delay_ms(1000); //delay
}
}
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We are now going to compile this code to generate the hex file and we will load same on the
Robot’s microcontroller. Select “Build” menu and click on “Rebuild All”. It will compile the
“buzzer_test.c” code and will generate “buzzer_test.hex” file for the robot’s microcontroller.
Figure 2.24
You can verify successful compilation in the bottom most “Build” window of the AVR Studio.
Figure 2.25
You can also verify that “buzzer_test.hex” file is generated in the “default” folder inside the
project folder you have selected.
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2.5 Debugging the code in AVR studio
After successful compilation of the code we can debug the code by AVR Debugger provided by
AVRStudio. Here is the illustration of debugging of code given in Exp1 (buzzer ON-OFF
folder).
Click on Debug tab in the menu and click on “Start Debugging”.
Figure 2.26
Now debugging mode is started and an arrow is visible at the first line of our main function from
where the debugging will start.
Figure 2.27
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Press “F11” key or “Step into” button
from the toolbar to start debugging statement by
statement. Processor details are visible at left window and the I/O port status is displayed at the
rightmost window.
Figure 2.28
By this way we can continuously monitor the bit changes in any of the registers of
microcontroller and debug the code before actually burning it to the microcontroller. PORTC bits
changes as per our commands and these changes can be seen in right window. After debugging is
done, select “Stop Debugging” from Debug tab.
Figure 2.29
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2.6 Loading your code on robot using AVR Boot loader from NEX Robotics
All AVR microcontrollers can be programmed using In System Programming (ISP), external
programmer or using boot loader. Advantage with the boot loader is that you don’t need any
external hardware to load .hex file on the microcontroller. It also protects robot’s hardware from
possible damage due to static electricity and prevents any accidental changes in the fuse settings
of the microcontroller.
2.6.1 Boot loader operating principle
If Bootloader firmware is loaded on the microcontroller, it allows in system programming
directly via serial port without any need for the external ISP programmer. Code responsible for
In System Programming via serial port (boot loader) resides in the configurable boot memory
section of the microcontroller. When signaled using external switch while resetting the
microcontroller it gets active and waits for communication from the PC for copying .hex file on
the microcontroller’s flash memory. PC sends the .hex file to the microcontroller. Code residing
in the boot section loads the .hex file on the microcontroller’s flash memory. After the boot
loading process is complete, newly loaded code can be executed by pressing reset. Once the code
is loaded on the microcontroller UART is free and can be used for other applications. Bootloader
get invoked only if boot switch is kept pressed while microcontroller is reset using reset switch.
Note:
Bootloader code is loaded on the ATMEGA2560 of the Fire Bird V robot using ISP programmer.
It is recommended that you only use Bootloader for the robot. If you use ISP programmer with
the robot then boot section code might get erased and robot will no longer support boot loading.
2.6.2 Programming the robot via Bootloader from NEX Robotics
.hex file can be loaded on the robot via serial port or USB port of the Fire Bird V robot. Robot is
shipped with the bootloader to program robot via USB port.
USB port of the Fire Bird V robot is connected to the UART 2 of the ATMEGA2560
microcontroller via FT232 USB to serial converter. You need to install drivers for FT232 USB to
serial converter on the PC before bootloading.
2.6.3 Installing drivers of FT232 USB to Serial Converter
Steps to install drives for FT232 USB to Serial Converter are covered in detail in the section 6.5
of the Hardware Manual. To identify and change the COM port number, refer to section 6.6 of
the Hardware Manual.
Important:
1. If COM port number is set to more than 8 by the PC then you have to change it in the
range of COM 2 to COM 8 else AVR Bootloader will not program the robot. For
changing COM port number, refer to section 6.6 of the Hardware Manual.
2. When using USB port for the communication, for proper operation first turn on the robot
then insert the USB cable in the robot. We have to follow this sequence because USB to
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serial converter chip is powered by USB. If any fault occurs then turn off the robot and
remove the USB cable and repeat the same procedure.
2.6.4 Installing Bootloader GUI on the PC
Step 1:
Copy “AVR Bootloader” folder which is located in the “Software and Drivers” folder of the
documentation CD to the PC and click on the “setup” application file (not on AVR Bootloader
Setup).
Figure 2.30
Step 2:
Follow the installation steps to complete the installation.
Figure 2.31
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Figure 2.32
Figure 2.33
2.6.5 Using AVR Bootloader
Step 1:
Go to Start Menu and click on “AVR Bootloader”. AVR Bootloader software will start.
Figure 2.34
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Figure 2.35
Step 2:
Figure 2.36
In this step we will configure port settings, select the microcontroller and .hex file which is to be
loaded on the robot.
1. Make sure that drivers for FT232 USB to serial converter are installed.
2. FT232 is connected to the UART2 of the microcontroller by jumper J1 on the
ATMEGA2560 microcontroller board. For more details refer to section 6.3 of the
Hardware Manual.
3. Turn on the Robot.
4. Connect USB wire between Robot and the PC and wait for 2 seconds.
5. AVR Bootloader software will auto detect the COM port number.
6. Click on the COM port number. It will show the detected COM port numbers. If multiple
COM port numbers are detected then to identify COM port number associated with the
Robot, refer to section 6.6 in the Hardware Manual.
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7. If Robot’s COM port number is more than COM8 then change it to any COM port
number between COM1 to COM8.
8. Set the Baud rate at 115200 bps.
9. Select ATMEGA2560 microcontroller
10. Browse for the target .hex file.
Now we are ready to load .hex file on the robot.
Step 3:
In this step we will load the .hex file on the robot.
1. First press the boot switch (switch on the right). Press and release reset switch with time
interval of 1 second while continuously pressing the boot switch. Bootloader is written is
such a way that when reset switch is pressed while holding PE7 low, ATMEGA2560 will
go in to bootloading mode.
2. Press program button on the GUI. With in 2 seconds .hex file loading will start. You can
see the activity on the TX and RX LEDs of the FT232 USB to Serial Converter on the
ATMEGA2560 microcontroller adaptor board. These LEDs are located just below the
FT232 USB to Serial Converter chip. To find the location of the TX and RX LEDs refer
to figure 3.58 in the Hardware Manual.
3. Figure 2.37 shows the comments in the message box after successfully programming the
ATMEGA2560 microcontroller on the robot.
Figure 2.37
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After successfully programming following text will appear in message box:
Serial port timeout set to 5 sec.
Found AVRBOOT on COM7!
Entering programming mode...
Parsing XML file for device parameters...
Parsing '.\ATmega2560.xml'...
#######
Saving cached XML parameters...
Signature matches device!
Erasing chip contents...
Reading HEX input file for flash operations...
##############################################################################
##############################################################################
##############################################################################
#####
Programming Flash contents...
Using block mode...
###############
Reading Flash contents...
Using block mode...
###############
Comparing Flash data...
Equal!
Leaving programming mode...
Note:
Loading bootloader on the ATMEGA2560 microcontroller will be covered in the Section 2.11
after introduction to ISP programmers for the ATMEGA2560 microcontroller.
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2.7 Correct Jumper setting before loading hex file on the robot using ISP
programmer
All AVR microcontrollers can be programmed by using external In System Programmer. In the
manual we are going to cover AVRISP mkII from ATMEL and AVR USB programmer NRUSB-006 from NEX Robotics for In System Programming (ISP).
For ATMEGA2560 (master) and ATMEGA8 (slave) ISP is done via their SPI port. Both
microcontrollers also talk with each other using SPI bus where ATMEGA2560 acts as master
and ATMEGA8 acts as slave. Order to load the .hex file on these microcontrollers; we need to
disconnect the SPI bus connection between these microcontrollers by removing three Jumpers
marked by J4 on the ATMEGA2560 microcontroller socket. For more details on the jumpers
refer to section 3.19.6 of the Hardware Manual.
Refer to figure 2.38 and 2.39 for the correct jumper settings before proceeding to ISP. Figure
2.40 shows the ISP socket for the ISP programming.
Figure 2.38: Correct jumper setting before proceeding to ISP
Figure 2.39: Incorrect jumper setting before proceeding to ISP
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Figure 2.40: ISP socket on the ATMEGA2560 microcontroller adaptor board
Note:
ATMEGA8 slave microcontroller is used for collecting analog data from IR proximity sensors 6,
7, 8, Robot current sense (if ACS712 current sensor is installed), extended white line sensor
channels 4, 5, 6, 7 and pin on the servo expansion port. If you are not using these sensors then for
convenience you can keep jumper J4 disconnected. If you want to access these sensor values
then you have to connect jumper J4.
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2.8 Loading your code on the robot using ATMEL’s AVRISP mkII
programmer
AVRISP mkII programmer from the ATMEL is the most versatile programmer. It is very easy to
use and has more features. It is the most recommended programmer for the robot after AVR
Bootloader from NEX Robotics.
Figure 2.41: AVRISP mkII
Step 1:
1. Connect AVRISP mkII to the PC. It will install driver automatically provided that USB
driver installation option is selected while installing AVR Studio. For more details refer
to figure 2.13.
2. Start AVR Studio
3. Go to “Tools” tab and click on “Program AVR”. Select connect option.
4. Window as shown in figure 2.43 will open.
Figure 2.42
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Figure 2.43
5. Select platform as AVRISP mkII and Port as USB Port and press connect.
6. Window as shown in Figure 2.44 will appear.
Figure 2.44
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Step 2:
Connecting AVRISP mkII with the robot
1. AVRISP mkII use 6 pin FRC connector for ISP, while Fire Bird V robot uses 10 pin FRC
connector for programming. We need to use AVRISP adaptor to convert 6 pin to 10 pin
connector. Figure 2.45 shows the 6 to 10 pin converter for the In System Programming.
2. Connect AVRISP adaptor between robot and AVRISP mkII. Insert 10 pin FRC connector
in the Fire Bird V ATMEGA2560 robot and turn the power on. For ISP port location and
other precautions refer to section 2.7.
3. Turn on the robot
Figure 2.45: In System Programming
Step 3:
Reading the microcontroller signature
Follow Step 4 if you are connecting AVRISP mkII with the robot for the first time or if any
problem occurs during programming.
1. Go to Main tab
2. Select “ATMEGA2560” microcontroller.
3. Click on the “Read Signature” button.
4. It will read the signature and if its matches with the microcontroller signature, we will get
the confirmation as “Signature matches selected device” as shown in the below window.
Now we are ready to load hex file on the robot.
Figure 2.46
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If ISP does not work properly then try to reduce the ISP frequency and try it again by clicking on
the “Settings” button which is located inside the “Programming Mode and Target Settings
frame”. Refer to figure 2.47.
Figure 2.47: Changing ISP frequency if required
Note:
If you want to load program at faster speed you can increase the ISP frequency.
If you notice any instability while programming then reduce the ISP frequency.
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Step 4:
Loading .hex file on the microcontroller
1. Go to “Program” tab.
2. Check on Erase device before programming and Verify device after programming check
box.
3. Browse and select the desired hex file in the flash section
4. Press “Program” button
5. Look at the comments at the bottom to verify that hex file is loaded in the flash.
Figure 2.48
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2.9 Fuse settings for ATMEGA2560 (Master) microcontroller
All the microcontroller’s Fuse settings are factory set at the NEX Robotics before shipping the
robot. Do not change them. This information is only given for the reference.
All the Fuse settings are done using AVRISP mkII programmer. For starting AVRISP mkII refer
to section 2.8.
To check the fuse settings click on the Fuse tab. Following window shown in figure 2.49 will
appear. To verify the fuse settings press “Read”. To write fuse settings after modifications press
“Program”. Make sure that “Auto Read”, “Smart warning” and “Verify after programming” are
checked.
Upon clicking on the “SUT CKSEL” it will extend the clock options as shown in figure 2.50. In
the “SUT CKSEL” select “Ext. Crystal Osc. 8.0- MHz; Start-up time: 16K CK + 65ms”
Figure 2.49
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Figure 2.50: Fuse settings of ATMEGA2560 microcontroller
Following fuse settings are done:
1. Brown-out detection set at 2.7V (checked)
2. JTAG enabling is disabled (JTAGEN) (unchecked)
3. Boot size is selected at 2408 bytes.
4. BOOTRST is enabled. This will enable the boot mode detection at the PE7 of the
microcontroller it PE7 is held logic low while microcontroller is reset. (checked)
5. Clock option (SUT CKSEL) set as external crystal of more than 8MHz i.e. “Ext. Crystal
Osc. 8.0- MHz; Start-up time: 16K CK + 65ms”
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2.10 Fuse settings for ATMEGA8 (Slave) microcontroller
All the microcontroller’s Fuse settings are factory set at the NEX Robotics before shipping the
robot. Do not change them. This information is only given for the reference.
All the Fuse settings are done using AVRISP mkII programmer. For starting AVRISP mkII refer
to section 2.8.
To check the fuse settings click on the Fuse tab. Following window shown in figure 2.51 will
appear. To verify the fuse settings press “Read”. To write fuse settings after modifications press
“Program”. Make sure that “Auto Read”, “Smart warning” and “Verify after programming” are
checked.
Figure 2.51
Following fuse settings are done:
1. Brown-out detection set at 2.7V (checked)
2. Clock option (SUT CKSEL) set as internal RC oscillator set at 8MHz i.e. “Int. RC Osc.
8MHz; Start-up time: 6CK + 0ms”
Important:
1. Never ever ever ever … select external crystal oscillator option in “SUT_CKSEL” for the
ATMEGA8 microcontroller. As ATMEGA8 doesn’t have the crystal oscillator it will not
able to respond to anything from any device and we have to replace the microcontroller.
2. Before loading hex file or reading fuse settings ensure that jumpers at J4 are open as
shown in figure 2.38 and are not as shown in figure 2.39.
Firmware for the ATMEGA8 (Slave microcontroller)
Firmware for the ATMEGA8 microcontroller is located in the folder “GUI and Related
Firmware \ ATMEGA8 hex file”
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2.11 Loading bootloader code on the ATMEGA2560 microcontroller
Fire Bird V ATMEGA2560 robot is factory shipped with the bootloader. If you do In System
Programming using any ISP programmers then bootloader will get erased. To load the
bootloader you will need the ISP programmer.
You need to load “M2560-14_7456MHz. USB-UART 2.a90” on the ATMEGA2560
microcontroller. This file is located in the documentation CD with the following path: “\Software
and Drivers\AVR Bootloader\AVR Bootloader Microcontroller firmware”
To load this file follow the exactly same procedure as described in the step 4 of the section 2.8.
Make sure that ATMEGA2560 has exactly the same fuse settings as described in the section 2.9.
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2.12 Loading your code on the robot using AVR USB programmer from NEX
Robotics
USBasp, is an USB port based programmer from NEX Robotics. This programmer requires
avrdude.exe file which comes with WINAVR. So installation of WINAVR is necessary for this
programmer. How to load this hex file is covered in detail in the programmer’s documentation. It
is located in the “AVR USB Programmer Documentation” folder inside the documentation CD.
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3. Input / Output Operations on the Robot
ATMEGA2560 microcontroller has ten 8 bit ports from PORT A to PORT F and PORT H to
PORT L (no PORT I) and PORT G has 6 bits. Input/output operations are the most essential,
basic and easy operations.
We need frequent I/O operations mainly to do following tasks:
Function
Robot Direction control
LCD display control
On Board Interrupt Switch
Buzzer control
Sharp & White line sensor control
Side Sharp Enable
IR Proximity Analog sensor
enable
Pins
PA3 to PA0
PC0 to PC2
PC4 to PC7
PE7(INT7)
PC3
PG2
PH2
PH3
Input / Output
Output
Recommended
Initial State
Logic 0
Input / Output
Logic 0
Input
Output
Output
Output
Pulled up*
Logic 0
Logic 1 **
Logic 1***
Output ****
Logic 1
Output
Table 3.1
Note:
* In the AVR microcontrollers while pin is used as input it can be pulled up internally by using
software enabled internal pull-up resistor. This internal pull-up as name indicates pulls up the
floating pin towards Vcc. This makes input pin less susceptible to noise.
** Power to the Sharp IR range sensor 2, 3, 4 and red LEDs of the white line sensor can be
turned on permanently by jumper 1 marked as J1 on the main board. In order to control
illumination by microcontroller, jumper J1 must be removed. For more details refer to the section
3.10, 3.11 and 3.12 of the Fire Bird V Hardware Manual.
*** Power to the Sharp IR range sensor 1, 5 can be turned on permanently by jumper 3 marked
as J3 on the main board. In order to control illumination by microcontroller jumper J3 must be
removed. For more details refer to the section 3.10, 3.11 and 3.12 of the Fire Bird V Hardware
Manual.
**** Fire Bird V has eight IR proximity Analog sensors out of which five are interfaced directly
to ATMEGA2560. Power to these eight IR proximity sensors can be turned on permanently by
jumper 2 marked as J2 on the main board. In order to control illumination by microcontroller
jumper J2 must be removed. For more details refer to the section 3.10, 3.11 and 3.12 of the Fire
Bird V Hardware Manual.
By disabling these sensors we can reduce current consumption by about 300mA and also allow
many robots work in the same field without interfering with each other’s sensors by turning them
on and off in a predetermined schedule which can be synchronized via wireless communication
between these robots using XBee wireless module.
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3.1 Registers for using PORTs of the ATMEGA2560 microcontroller
Each pin of the port can be addressed individually. Each pin individually can be configured as
input or as output. While pin is input it can be kept floating or even pulled up by using internal
pull-up. While pin is in the output mode it can be logic 0 or logic 1. To configure these ports as
input or output each of the port has three associated I/O registers. These are Data Direction
Register (DDRx), Port Drive Register (PORTx) and Port pins register (PINx) where ‘x’ is A to L
(except I) indicating particular port name.
A. Data Direction Register (DDRx)
The purpose of the data direction register is to determine which bits of the port are used for input
and which bits are used for output. If logic one is written to the pin location in the DDRx, then
corresponding port pin is configured as an output pin. If logic zero is written to the pin location
in the DDRx, then corresponding port pin is configured as an input pin.
DDRA = 0xF0; //sets the 4 MSB bits of PORTA as output port and
//4 LSB bits as input port
B. Port Drive Register (PORTx)
If the port is configured as output port, then the PORTx register drives the corresponding value
on output pins of the port.
DDRA = 0xFF; //set all 8 bits of PORTA as output
PORTA = 0xF0; //output logic high on 4 MSB pins and logic low on 4 LSB pins
For pins configured as input, we can instruct the microcontroller to apply a pull up register by
writing logic 1 to the corresponding bit of the port driver register.
DDRA = 0x00; //set all 8 bits of PORTA as input
PORTA = 0xF0; //pull-up registers are connected on 4 MSB pins and 4 LSB pins are floating
C. Port pins register (PINx)
Reading from the input bits of port is done by reading port pin register
x = PINA; //read all 8 pins of port A
DDRx
PORTx
I/O
Pull-up
Comments
0
0
Input
No
0
1
Input
Yes
1
1
0
1
Output
Output
No
No
floating input
Will source current if externally pulled
low
Output Low (Sink)
Output High (source)
Table 3.2
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Note:
• ‘X’ represents port name – A, B, C, D, E, F, G, H, J, K, L.
• Tri-State is the floating pin condition.
• For more details, refer to ATMEGA2560 datasheet which is located in the “Datasheets”
folder in the documentation CD.
Example:
Make PORTA 0-3 bits as output and PORTA 4-7 bits input.
Add pull-up to pins PORTA 4 and PORTA 5.
Output of PORTA 0 and PORTA 2 = 1; PORT A 1 and PORT A 3 = 0;
Pin
DDRA
PORTA
Status
PA7
0 (i/p)
0
i/p
Floating
PA6
0 (i/p)
0
i/p
Floating
PA5
0 (i/p)
1 (↑)
i/p
Pull-up
PA4
0 (i/p)
1 (↑)
i/p
Pull-up
PA3
1 (o/p)
0
o/p
Low
PA2
1 (o/p)
1
o/p
High
PA1
1 (o/p)
0
o/p
Low
PA0
1 (o/p)
1
o/p
High
Table 3.3
{
unsigned char k;
DDRA = 0x0F; //Make PA4 to PA7 pins input and PA0 to PA3 pins output
PORTA = 0x35; //Make PA7, PA6 floating; PA5, PA4 pulled-up; PA2, PA0 logic 0,
PA3, PA1 logic 1;
k = PINA; //Reads all the data from PORTA
while (1);
}
Figure 3.1: I/O pin equivalent schematic.
Source: ATMEGA2560 datasheet
All port pins have individually selectable pull-up resistors with a supply-voltage invariant
resistance. All I/O pins have protection diodes to both VCC and Ground as indicated in Figure.
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D. To disable pull-ups of all the ports we need to set Bit 2 of SFIOR to logic one.
Special Function I/O register – SFIOR
Pin
Read/ Write
Initial Val
TSM
R/W
0
R
0
R
0
R
0
ACME
R/W
0
PUD
R/W
0
PSR0
R/W
0
PSR321
R/W
0
Table 3.4
Bit 2-PUD: Pull-Up Disable
When this bit is written to one, the pull-ups in all the I/O ports are disabled even if the DDRxn
and PORTxn Registers are configured to enable the pull-ups ({DDRxn, PORTxn} = 0b01).
E. Toggling the Pin
Writing a logic one to PINxn toggles the value of PORTxn, independent on the value of DDRxn.
Note that the SBI instruction can be used to toggle one single bit in a port. Where ‘x’ is the port
name and ‘n’ is the bit number.
3.2 ATMEGA2560 microcontroller pin configuration
PIN
NO
Pin name
1
(OC0B)PG5
2
3
RXD0/PCINT8/PE0
TXD0/PE1
4
XCK0/AIN0/PE2
5
6
7
8
OC3A/AIN1/PE3
OC3B/INT4/PE4
OC3C/INT5/PE5
T3/INT6/PE6
9
CLK0/ICP3/INT7/ PE7
10
11
VCC
GND
12
RXD2/PH0
13
TXD2/PH1
14
XCK2/PH2
15
OC4A / PH3
16
OC4B / PH4
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USED FOR
Slave Select (SS) of the SPI expansion port on the main
board (refer to figure 3.5)
UART 0 receive for XBee wireless module (if installed)
UART 0 transmit for XBee wireless module (if installed)
GPIO* (Available on expansion slot of the microcontroller
socket)
PWM output for C2 motor drive
External Interrupt for the left motor’s position encoder
External Interrupt for the right motor’s position encoder
External Interrupt for the C2 motor’s position encoder
External Interrupt for Interrupt switch on the
microcontroller board, External Interrupt for the C1 motor’s
position encoder, Connection to TSOP1738 if pad is
shorted ********
5V
Ground
UART 2 receives for USB Communication.
For more details refer to section 3.19.7
UART 2 transmit for USB Communication.
For more details refer to section 3.19.7
Sharp IR ranges sensor 1and 5 enable / disable.
Turns off these sensors when output is logic 1 *******
IR proximity sensors 1 to 8 enable / disable.
Turns off these sensors when output is logic 1 *******
GPIO* (Available on expansion slot of the microcontroller
Status
-Default
Default
Output
Input
Input
Input
Input
Default
Default
Output
Output
--
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socket)
17
18
19
20
21
22
23
24
OC4C / PH5
OC2B / PH6
SS/PCINT0/PB0
SCK/PCINT1/PB1
MOSI/PCINT2/PB2
MISO/PCINT3/PB3
OC2A/PCINT4/PB4
OC1A/PCINT5/PB5
Servo Pod GPIO
PWM for Servo motor 1. ***
Output
Output
Input
-Output
25
OC1B/PCINT6/PB6
PWM for Servo motor 2. ***
Output
PWM for Servo motor 3. ***
Output
ISP (In System Programming), SPI Communication with
ATMEGA8 **, Connection to the SPI port on the main
board
---
27
28
29
30
OC0A/OC1C/PCINT7/
PB7
T4/PH7
TOSC2/PG3
TOSC1/PG4
RESET
Microcontroller reset
31
VCC
5V
32
33
34
35
36
37
GND
XTAL2
XTAL1
ICP4/PL0
ICP5/PL1
TS/PL2
Ground
38
OC5A/PL3
PWM for left motor.
Output
39
OC5B/PL4
PWM for right motor.
Output
40
OC5C/PL5
PWM for C1 motor.
Output
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
PL6
PL7
SCL/INT0/PD0
SDA/INT1/PD1
RXD1/INT2/PD2
TXD1/INT3/PD3
ICP1/PD4
XCK1/PD5
T1/PD6
T0/PD7
PG0/WR
PG1/RD
PC0
PC1
PC2
PC3
PC4
PC5
PC6
GPIO* (Available on expansion slot of the microcontroller
socket)
----Default
Default
------Output
Output
Output
Output
Output
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GPIO (Available On Expansion Slot)
--
RTC (Real Time Clock)****
Crystal 14.7456 MHz
GPIO (Available on expansion slot of the microcontroller
socket)
I2C bus / GPIOs (Available on expansion slot of the
microcontroller socket)
UART1 receive for RS232 serial communication
UART1 transmit for RS232 serial communication
GPIO* (Available on expansion slot of the microcontroller
socket)
GPIO* (Available on expansion slot of the microcontroller
socket)
LCD control line RS (Register Select)
LCD control line RW(Read/Write Select)
LCD control line EN(Enable Signal)
Buzzer
LCD data lines (4-bit mode)
----
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60
61
62
63
64
65
66
67
68
69
PC7
VCC
GND
PJ0/RXD3/PCINT9
PJ1/TXD3/PCINT10
PJ2/XCK3/PCINT11
PJ3/PCINT12
PJ4/PCINT13
PJ5/PCINT14
PJ6/PCINT15
70
PG2/ALE
71
72
73
74
75
76
77
78
PA7 C2-2
PA6 C2-1
PA5 C1-2
PA4 C1-1
PA3
PA2
PA1
PA0
79
PJ7
80
81
VCC
GND
Sharp IR ranges sensor 2, 3, 4 and red LEDs of white line
sensor 1, 2, 3 disable. *******
Turns off these sensors when output is logic 1
Logic input 2 for C2 motor drive
Logic input 1 for C2 motor drive
Logic input 2 for C1 motor drive
Logic input 1 for C1 motor drive
Logic input 1 for Right motor (Right back)
Logic input 2 for Right motor (Right forward)
Logic input 2 for Left motor (Left forward)
Logic input 1 for Left motor (Left back)
LED Bar Graph and GPIO* (Available on expansion slot
of the microcontroller socket)
5V
Ground
82
PK7/ADC15/PCINT23
ADC Input For Servo Pod 2
83
PK6/ADC14/PCINT22
ADC Input For Servo Pod 1
84
PK5/ADC13/PCINT21
ADC input for Sharp IR range sensor 5
85
PK4/ADC12/PCINT20
ADC input for Sharp IR range sensor 4
86
PK3/ADC11/PCINT19
ADC input for Sharp IR range sensor 3
87
PK2/ADC10/PCINT18
ADC input for Sharp IR range sensor 2
88
PK1/ADC9/PCINT17
ADC input for Sharp IR range sensor 1
89
PK0/ADC8/PCINT16
ADC input for IR proximity analog sensor 5
90
PF7(ADC7/TDI)
ADC input for IR proximity analog sensor 4*****
91
PF6/(ADC6/TD0)
ADC input for IR proximity analog sensor 3*****
92
PF5(ADC5/TMS)
ADC input for IR proximity analog sensor 2*****
93
PF4/ADC4/TCK
ADC input for IR proximity analog sensor 1*****
94
PF3/ADC3
ADC input for white line sensor 1
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5V
Ground
LED bargraph display and GPIO* (Available on expansion
slot of the microcontroller socket)
Output
Output
Output
Output
Output
Output
Output
Output
Output
Output
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Input
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95
PF2/ADC2
ADC input for white line sensor 2
96
PF1/ADC1
ADC input for white line sensor 3
97
PF0/ADC0
ADC input for battery voltage monitoring
98
99
100
AREF
GND
AVCC
ADC reference voltage pin (5V external) ******
Ground
5V
(Floating)
Input
(Floating)
Input
(Floating)
Input
(Floating)
Table 3.5: ATMEGA2560 microcontroller pin connections
* Not used pins are by default initialized to input and kept floating. These pins are available on
the expansion slot of the ATMEGA2560 microcontroller adaptor board. Some pins are especially
reserved for servo motor interfacing for the Fire Bird V Hexapod robot.
** MOSI, MISO, SCK and SS pins of ATMEGA2560 are associated to the ISP (In System
programming) port as well as the SPI interface to ATMEGA8. J4 needs to be disconnected
before doing ISP. To communicate with ATMEGA8 jumper J4 needs to be in place. For more
details refer to section 3.19.6.
*** PORTB pin5, 6, 7 are OC1A, OC1B, OC1C of the Timer1. These pins are connected to the
servo motor sockets S1, S2, S3 on the microcontroller adaptor board.
**** External Crystal of 32 KHz is connected to the pins PG3 and PG4 to generate clock for
RTC (Real Time Clock).
***** For using Analog IR proximity (1, 2, 3 and 4) sensors short the jumper J2. To use JTAG
or interface external analog sensors via expansion slot of the microcontroller socket remove
these jumpers.
****** AREF can be obtained from the 5V microcontroller or 5V analog reference generator IC
REF5050 (optional). For more details refer to section 3.19.9.
******* Sensor’s switching can be controlled only is if corresponding jumpers are open. For
more details refer to section 3.11 and 3.12.
J2: Sharp IR range sensor 2, 3, 4 and red LEDs of white line sensors;
J3: Sharp IR range sensor 1, 5;
J4: IR proximity sensors 1 to 8;
******** External interrupt from the position encoder C1 is disabled by removing pin 2 of the
CD40106 Schmitt trigger inverter buffer to avoid its wire anding with the interrupt switch.
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3.3 Application example Buzzer Beep
Located in the folder “Experiments \ Buzzer_Beep” folder in the documentation CD.
In the previous chapter, we have loaded buzzer beep code in Fire Bird V. Now we will see in
detail the structure of this code.
This experiment demonstrates the simple operation of Buzzer ON/OFF with one second delay.
Buzzer is connected to PORTC 3 pin of the ATMEGAM2560
Concepts covered: Output operation, generating exact delay
Note: Make sure that in the configuration options following settings are done for proper
operation of the code
Microcontroller: atmega2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
//Buzzer is connected at the third pin of the PORTC
//To turn it on make PORTC 3rd pin logic 1
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
//Function to initialize Buzzer
void buzzer_pin_config (void)
{
DDRC = DDRC | 0x08;
PORTC = PORTC & 0xF7;
}
//Setting PORTC 3 as output
//Setting PORTC 3 logic low to turnoff buzzer
void port_init (void)
{
buzzer_pin_config();
}
void buzzer_on (void)
{
unsigned char port_restore = 0;
port_restore = PINC;
port_restore = port_restore | 0x08;
PORTC = port_restore;
}
void buzzer_off (void)
{
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unsigned char port_restore = 0;
port_restore = PINC;
port_restore = port_restore & 0xF7;
PORTC = port_restore;
}
void init_devices (void)
{
cli(); //Clears the global interrupts
port_init();
sei(); //Enables the global interrupts
}
//Main Function
int main(void)
{
init_devices();
while(1)
{
buzzer_on();
_delay_ms(1000);
buzzer_off();
_delay_ms(1000);
}
}
//delay
//delay
In this code, first three lines represent the header file declaration. The # include directive is used
for including header files in the existing code. The syntax for writing header file is as follows:
#include <avr/io.h>
This # include directive will add the already existing io.h header file stored in avr folder under
WinAVR folder. The same way other header files are also included in the main program so that
we can use various utilities defined in the header files.
In all the codes we will configure pins related to any particular module in the xxxx_pin_config()
functions. In this example code we have used the function buzzer_pin_config(). Buzzer is
connected to the PORTC 3 pin of the microcontroller. PORTC 3 is configured as output with the
initial value set to logic 0 to keep buzzer off at the time of port initialization. All the
xxxx_pin_config() functions will be initialized in the port_init() function in all the codes as a
convention. Function init_devices() will be used to initialize all the peripherals of the
microcontroller as a convention.
In the above code buzzer is turned on by calling function buzzer_on().
_delay_ms(1000) introduces delay of 1 second.
Buzzer is turned off by calling function buzzer_off().
Again _delay_ms(1000) introduces delay of 1 second.
All these statements are written in while(1) loop construct to make buzzer on-off periodically.
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3.4 Application example Simple Input – Output operation
Located in the folder “Experiments \ I-O Interfacing” folder in the documentation CD.
This experiment demonstrates simple Input and Output operation. When switch is pressed buzzer
and bargraph LED display is turned on. When switch is opened buzzer and bargraph display are
turned off. Refer to folder “Experiments \ I-O Interfacing” folder in the documentation CD to
look at the program.
Concepts covered: Input and Output operations
Connections:
Buzzer: PORTC 3
LED bargraph: PORTJ 7 to PORTJ 0
Interrupt switch: PORTE 7
Note:
1. Make sure that in the configuration options following settings are done for proper operation of
the code
Microcontroller: ATMEGA2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
2. Jumper J3 is in place to enable LED bargraph display on the ATMEGA2560 microcontroller
adaptor board
3.5 Robot direction control
Located in the folder “Experiments \ Motion_Control_Simple” folder in the documentation CD.
Hardware aspects of the motion control are covered in detail in the section 3.8 and 3.9 of the
Hardware Manual. Robot’s motors are controlled by L293D motor controller from ST
Microelectronics. Using L293D, microcontroller can control direction and velocity of both of the
motors. To change the direction appropriate logic levels (High/Low) are applied to IC L293D’s
direction pins. Velocity control is done using pulse width modulation (PWM) applied to Enable
pins of L293D IC. For more information, refer to section 3.8 and 3.9 of the Hardware Manual.
Figure 3.2
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DIRECTION
LEFT
BWD
(LB)
PA0
(L1)
LEFT
FWD(LF)
PA1 (L2)
RIGHT
FWD(RF)
PA2 (R1)
RIGHT
BWD(RB)
PA3 (R2)
FORWARD
0
1
1
0
REVERSE
1
0
0
1
0
1
0
1
1
0
1
0
As per velocity
requirement
SOFT RIGHT(Left wheel
forward,, Right wheel stop)
0
1
0
0
As per velocity
requirement
SOFT LEFT(Left wheel
stop, Right wheel forward,)
0
0
1
0
As per velocity
requirement
SOFT RIGHT 2 (Left wheel
stop, Right wheel backward)
0
0
0
1
As per velocity
requirement
SOFT LEFT 2 (Left wheel
backward, Right wheel stop)
1
0
0
0
As per velocity
requirement
HARD STOP
0
0
0
0
As per velocity
requirement
SOFT STOP (Free running
stop)
X
X
X
X
0
RIGHT (Left wheel
forward, Right wheel
backward)
LEFT(Left wheel backward,
Right wheel forward,)
PWM
PL3 (PWML) for
left motor
PL4 (PWMR) for
right motor
As per velocity
requirement
As per velocity
requirement
As per velocity
requirement
Table 3.6: Logic levels for robot motion control
Figure 3.3
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Note:
• All the soft turns should be used when you need more accuracy during turning
• Soft left 2 and Soft right 2 motions are very useful in grid navigation.
Application example: Robot direction control
Located in the folder “Experiments \ Motion_Control_Simple” folder in the documentation CD.
This experiment demonstrates simple motion control.
Concepts covered: Simple motion control using I-O interfacing
There are two components to the motion control:
1. Direction control using pins PORTA0 to PORTA3
2. Velocity control by PWM on pins PL3 and PL4 using OC5A and OC5B of timer 5.
In this experiment for the simplicity PL3 and PL4 are kept at logic 1.
Connections:
Microcontroller Pin
PL3 (OC5A)
PL4 (OC5B)
PA0
PA1
PA2
PA3
Function
Pulse width modulation for the left motor (velocity control)
Pulse width modulation for the right motor (velocity control)
Left motor direction control
Left motor direction control
Right motor direction control
Right motor direction control
Table 3.7: Pin functions for the motion control
Note:
1. Make sure that in the configuration options following settings are done for proper operation of
the code
Microcontroller: ATMEGA2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
2. Auxiliary power can supply current up to 1 Ampere while Battery can supply current up to 2
Ampere. When both motors of the robot changes direction suddenly without stopping, it
produces large current surge. When robot is powered by Auxiliary power which can supply only
1 Ampere of current, sudden direction change in both the motors will cause current surge which
can reset the microcontroller because of sudden fall in voltage. It is a good practice to stop the
motors for at least 0.5seconds before changing the direction. This will also increase the useable
time of the fully charged battery.
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3.6 Functions used by the robot for configuring various ports of the
ATMEGA2560 microcontroller
3.6.1 Buzzer
Buzzer is connected to the PORTC 3 pin of the microcontroller.
Buzzer is turned on of logic 1 is applied at the PORTC 3 pin. For more information on the
hardware refer to section 3.13 in the Hardware Manual.
3.6.1.1 buzzer_pin_config()
PORTC 3 pin is configured as output with the initial state set at logic 0 to keep the buzzer
off.
void buzzer_pin_config (void)
{
DDRC = DDRC | 0x08;
PORTC = PORTC & 0xF7;
}
//Setting PORTC 3 as output
//Setting PORTC 3 logic low to turnoff buzzer
3.6.1.2 buzzer_on()
Turns on the buzzer by setting PORTC 3 pin to logic 1.
void buzzer_on (void)
{
unsigned char port_restore = 0;
port_restore = PINC;
port_restore = port_restore | 0x08;
PORTC = port_restore;
}
3.6.1.3 buzzer_off()
Turns off the buzzer by setting PORTC 3 pin to logic 0.
void buzzer_off (void)
{
unsigned char port_restore = 0;
port_restore = PINC;
port_restore = port_restore & 0xF7;
PORTC = port_restore;
}
3.6.2 Interrupt switch
Interrupt switch is connected to the PORTE 7 pin of the microcontroller. It has 10Kohm external
pull-up resistor. When switch is pressed PORTE 7 pin is connected with the ground. Fore more
details on the hardware refer to the section 3.19.10 in the Hardware Manual.
Interrupt switch is used as general purpose input device. Interrupt switch is configured as input
with its internal pull-up resistor enabled.
void interrupt_switch_config (void)
{
DDRE = DDRE & 0x7F; //PORTE 7 pin set as input
PORTE = PORTE | 0x80; //PORTE7 internal pull-up enabled
}
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3.6.3 Bargraph LED display
Bargraph LED display is connected to the port J of the microcontroller. It can be used as general
purpose LED display to display data or information for debugging.
void LED_bargraph_config (void)
{
DDRJ = 0xFF; //PORT J is configured as output
PORTJ = 0x00; //Output is set to 0
}
Note: To use this display make sure that Jumper J3 is enabled on the microcontroller adaptor
board. For more details, refer to section 3.19.6 of the Hardware Manual.
3.6.4 Robot motion control
For more information on the hardware, refer to section 3.8 and 3.9 from the Hardware Manual
and table 3.7 for the hardware connection details, table 3.6 for control logic from this manual.
3.6.4.1 motion_pin_config()
Sets the directions and logic levels of the pins involved in the motion control.
void motion_pin_config (void)
{
DDRA = DDRA | 0x0F; //set direction of the PORTA 3 to PORTA 0 pins as output
PORTA = PORTA & 0xF0; // set initial value of the PORTA 3 to PORTA 0 pins to logic 0
DDRL = DDRL | 0x18; //Setting PL3 and PL4 pins as output for PWM generation
PORTL = PORTL | 0x18; //PL3 and PL4 pins are for velocity control using PWM
}
3.6.4.2 motion_set()
Used for setting appropriate logic values for controlling robots direction. It is called by other
functions to set robot’s direction.
void motion_set (unsigned char Direction)
{
unsigned char PortARestore = 0;
Direction &= 0x0F;
PortARestore = PORTA;
PortARestore &= 0xF0;
PortARestore |= Direction;
PORTA = PortARestore;
}
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// removing upper nibbel as it is not needed
// reading the PORTA's original status
// setting lower direction nibbel to 0
// adding lower nibbel for direction command and
// restoring the PORTA status
// setting the command to the port
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3.6.4.3 Robot direction set functions
Sets robot’s direction
void forward (void) //both wheels forward
{
motion_set(0x06);
}
void back (void) //both wheels backward
{
motion_set(0x09);
}
void left (void) //Left wheel backward, Right wheel forward
{
motion_set(0x05);
}
void right (void) //Left wheel forward, Right wheel backward
{
motion_set(0x0A);
}
void soft_left (void) //Left wheel stationary, Right wheel forward
{
motion_set(0x04);
}
void soft_right (void) //Left wheel forward, Right wheel is stationary
{
motion_set(0x02);
}
void soft_left_2 (void) //Left wheel backward, right wheel stationary
{
motion_set(0x01);
}
void soft_right_2 (void) //Left wheel stationary, Right wheel backward
{
motion_set(0x08);
}
void stop (void) //hard stop if PORTL 3 and PORTL 4 pins are at logic 1
{
motion_set(0x00);
}
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3.6.5 Functions for Robot’s sensors switching on / off
Using these function robots sensors can be switched on or off. Before using these functions,
make sure that Jumper 2, 3, 4 are open on the main board. For more details refer to the section
3.10, 3.11 and 3.12 0f the Hardware Manual.
Connections:
PORTG 2: Power control of Sharp IR Range sensor 2, 3, 4 and red LEDs of the white line
sensors
PORTH 2: Power control of Sharp IR Range sensor 1, 5
PORTH 3: Power control of IR Proximity sensors 1 to 8
Note: If Jumper 2, 3, 4 are open on the main board then setting logic 1 at the pin turns off the
corresponding set of sensors.
3.6.5.1 MOSFET_switch_config()
Sets direction of PORTG 2, PORTH 2 and PORTH 3 as output with initial value set to logic
0
void MOSFET_switch_config (void)
{
DDRH = DDRH | 0x0C; //make PORTH 3 and PORTH 1 pins as output
PORTH = PORTH & 0xF3; //set PORTH 3 and PORTH 1 pins to 0
DDRG = DDRG | 0x04; //make PORTG 2 pin as output
PORTG = PORTG & 0xFB; //set PORTG 2 pin to 0
}
3.6.5.2 Functions for controlling power delivered to the sensors
void turn_on_sharp234_wl (void)
//turn on Sharp IR range sensors 2, 3, 4 and white line sensor's red LED
{
PORTG = PORTG & 0xFB;
}
void turn_off_sharp234_wl (void)
//turn off Sharp IR range sensors 2, 3, 4 and white line sensor's red LED
{
PORTG = PORTG | 0x04;
}
void turn_on_sharp15 (void) //turn on Sharp IR range sensors 1,5
{
PORTH = PORTH & 0xFB;
}
void turn_off_sharp15 (void) //turn off Sharp IR range sensors 1,5
{
PORTH = PORTH | 0x04;
}
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void turn_on_ir_proxi_sensors (void) //turn on IR Proximity sensors
{
PORTH = PORTH & 0xF7;
}
void turn_off_ir_proxi_sensors (void) //turn off IR Proximity sensors
{
PORTH = PORTH | 0x08;
}
void turn_on_all_proxy_sensors (void)
// turn on Sharp 2, 3, 4, red LED of the white line sensors, Sharp 1, 5 and IR proximity sensor
{
PORTH = PORTH & 0xF3; //set PORTH 3 and PORTH 1 pins to 0
PORTG = PORTG & 0xFB; //set PORTG 2 pin to 0
}
void turn_off_all_proxy_sensors (void)
// turn off Sharp 2, 3, 4, red LED of the white line sensors Sharp 1, 5 and IR proximity sensor
{
PORTH = PORTH | 0x0C; //set PORTH 3 and PORTH 1 pins to 1
PORTG = PORTG | 0x04; //set PORTG 2 pin to 1
}
3.6.6 Functions for configuring Position encoder pins
3.6.6.1 left_encoder_pin_config()
//Function to configure INT4 (PORTE 4) pin as input for the left position encoder
void left_encoder_pin_config (void)
{
DDRE = DDRE & 0xEF; //Set the direction of the PORTE 4 pin as input
PORTE = PORTE | 0x10; //Enable internal pull-up for PORTE 4 pin
}
3.6.6.2 right_encoder_pin_config()
//Function to configure INT5 (PORTE 5) pin as input for the right position encoder
void right_encoder_pin_config (void)
{
DDRE = DDRE & 0xDF; //Set the direction of the PORTE 4 pin as input
PORTE = PORTE | 0x20; //Enable internal pull-up for PORTE 4 pin
}
3.6.7 Functions for configuring servo motor control pins
3.6.7.1 servo1_pin_config();
//Configure PORTB 5 pin for servo motor 1 operation
void servo1_pin_config (void)
{
DDRB = DDRB | 0x20; //making PORTB 5 pin output
PORTB = PORTB | 0x20; //setting PORTB 5 pin to logic 1
}
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3.6.7.2 servo2_pin_config();
//Configure PORTB 6 pin for servo motor 2 operation
void servo2_pin_config (void)
{
DDRB = DDRB | 0x40; //making PORTB 6 pin output
PORTB = PORTB | 0x40; //setting PORTB 6 pin to logic 1
}
3.6.7.3 servo3_pin_config();
//Configure PORTB 7 pin for servo motor 3 operation
void servo3_pin_config (void)
{
DDRB = DDRB | 0x80; //making PORTB 7 pin output
PORTB = PORTB | 0x80; //setting PORTB 7 pin to logic 1
}
3.6.8 lcd_port_config()
void lcd_port_config (void)
{
DDRC = DDRC | 0xF7; //all the LCD pin's direction set as output
PORTC = PORTC & 0x80; // all the LCD pins are set to logic 0 except PORTC 7
}
3.6.9 adc_pin_config()
void adc_pin_config (void)
{
DDRF = 0x00; //set PORTF direction as input
PORTF = 0x00; //set PORTF pins floating
DDRK = 0x00; //set PORTK direction as input
PORTK = 0x00; //set PORTK pins floating
}
3.6.10 spi_pin_config()
void spi_pin_config (void)
{
DDRB = DDRB | 0x07;
PORTB = PORTB | 0x07;
}
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4. Robot Position Control Using Interrupts
Fire Bird V incorporates various interrupt handling mechanisms such as timer overflow
interrupts, timer compare interrupts, serial interrupts for doing specific tasks. In this chapter, we
will have a brief overview of interrupt concept and will implement external hardware interrupts
for position estimation of robots using position encoders.
Interrupts interrupt the flow of the program and cause it to branch to ISR (Interrupt Service
Routine). ISR does the task that needs to be done when interrupt occurs. Whenever position
encoder moves by one tick it interrupts the microcontroller and ISR does the job of tracking
position count.
Each interrupt has a vector address assigned to it low in program memory. The compiler places
the starting address of the associated interrupt service routine and a relative jump instruction at
the vector location for each interrupt. When the interrupt occurs, the program completes
executing its current instruction and branches to the vector location associated with that interrupt.
The program then executes the relative jump instruction to the interrupt service routine (ISR) and
begins executing the ISR. For more information on the interrupt vectors refer to table 14.1 in the
ATMEGA2560 datasheet which is located in the “datasheet” folder in the documentation CD.
When an interrupt occurs, the return address is stored on the system stack. The RETI assembly
language instruction causes the return address to be popped off the stack and continue program
execution from the point where it was interrupted.
4.1 Using Interrupts
Interrupts needs to be initialized before they become active. Initializing interrupt is a three step
process. The first step is to select the trigger type for the interrupt. We are using falling edge
trigger. This is selected by setting bits in EICRA (INT3 to INT0) and EICRB (INT7 to INT4)
registers. Second step is to unmask the interrupt that we want to use in the EIMSK register. In
the third step we globally enable all the unmasked interrupts. To enable unmasked interrupts we
need to set global interrupt enable bit in the status register (SREG). This is done by instruction
“sei();”.
4.1.1 Registers involved
4.1.1.1 EICRA – External Interrupt Control Register A
Bit
Read / Write
Initial Value
7
ISC31
R/W
0
6
ISC30
R/W
0
5
ISC21
R/W
0
4
ISC20
R/W
0
3
ISC11
R/W
0
2
ISC10
R/W
0
1
ISC01
R/W
0
0
ISC00
R/W
0
Bits 7:0 – ISC31, ISC30 – ISC00, ISC00: External Interrupt 3 - 0 Sense Control Bits
The External Interrupts 3 - 0 are activated by the external pins INT3:0 if the SREG I-flag and
the corresponding interrupt mask in the EIMSK is set. The level and edges on the external
pins that activate the interrupts are defined in Table 4.1. Edges on INT3:0 are registered
asynchronously. Pulses on INT3:0 pins wider than 50 nanoseconds will generate an interrupt.
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Shorter pulses are not guaranteed to generate an interrupt. If low level interrupt is selected,
the low level must be held until the completion of the currently executing instruction to
generate an interrupt. If enabled, a level triggered interrupt will generate an interrupt request
as long as the pin is held low. When changing the ISCn bit, an interrupt can occur. Therefore,
it is recommended to first disable INTn by clearing its Interrupt Enable bit in the EIMSK
Register. Then, the ISCn bit can be changed. Finally, the INTn interrupt flag should be
cleared by writing a logical one to its Interrupt Flag bit (INTFn) in the EIFR Register before
the interrupt is re-enabled.
ISCn1
0
0
1
1
ISCn2
0
1
0
1
Description
The low level of INTn generates an interrupt request.
Any edge of INTn generates asynchronously an interrupt request.
The falling edge of INTn generates asynchronously an interrupt request.
The rising edge of INTn generates asynchronously an interrupt request.
Table 4.1: Interrupt Sense Control
Note:
• n = 0, 1, 2 or 3.
• When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its
Interrupt Enable bit in the EIMSK Register. Otherwise an interrupt can occur when the
bits are changed.
4.1.1.2 EICRB – External Interrupt Control Register B
Bit
Read / Write
Initial Value
7
ISC71
R/W
0
6
ISC70
R/W
0
5
ISC61
R/W
0
4
ISC60
R/W
0
3
ISC51
R/W
0
2
ISC50
R/W
0
1
ISC41
R/W
0
0
ISC40
R/W
0
Bits 7:0 – ISC71, ISC70 - ISC41, ISC40: External Interrupt 7 - 4 Sense Control Bits
The External Interrupts 7 - 4 are activated by the external pins INT7:4 if the SREG I-flag and
the corresponding interrupt mask in the EIMSK is set. The level and edges on the external
pins that activate the interrupts are defined in Table 4.2. The value on the INT7:4 pins are
sampled before detecting edges. If edge or toggle interrupt is selected, pulses that last longer
than one clock period will generate an interrupt. Shorter pulses are not guaranteed to generate
an interrupt. Observe that CPU clock frequency can be lower than the XTAL frequency if the
XTAL divider is enabled. If low level interrupt is selected, the low level must be held until
the completion of the currently executing instruction to generate an interrupt. If enabled, a
level triggered interrupt will generate an interrupt request as long as the pin is held low.
ISCn1
0
0
1
1
ISCn2
0
1
0
1
Description
The low level of INTn generates an interrupt request.
Any logical change on INTn generates an interrupt request
The falling edge between two samples of INTn generates an interrupt request.
The rising edge between two samples of INTn generates an interrupt request.
Table 4.2: Interrupt Sense Control
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Note:
• n = 7, 6, 5 or 4.
• When changing the ISCn1/ISCn0 bits, the interrupt must be disabled by clearing its
Interrupt Enable bit in the EIMSK Register. Otherwise an interrupt can occur when the
bits are changed.
• Compare table 4.1 and 4.2. Interrupt 0 to 3 and Interrupt 4 to 7 are bit different in nature.
4.1.1.3 EIMSK – External Interrupt Mask Register
Bit
Read / Write
Initial Value
7
INT7
R/W
0
6
INT6
R/W
0
5
INT5
R/W
0
4
INT4
R/W
0
3
INT3
R/W
0
2
INT2
R/W
0
1
INT1
R/W
0
0
INT0
R/W
0
Bits 7:0 – INT7:0: External Interrupt Request 7 - 0 Enable
When an INT7:0 bit is written to one and the I-bit in the Status Register (SREG) is set (one),
the corresponding external pin interrupt is enabled. The Interrupt Sense Control bits in the
External Interrupt Control Registers – EICRA and EICRB – defines whether the external
interrupt is activated on rising or falling edge or level sensed. Activity on any of these pins
will trigger an interrupt request even if the pin is enabled as an output. This provides a way
of generating a software interrupt.
4.1.1.4 EIFR – External Interrupt Flag Register
Bit
Read / Write
Initial Value
7
INT7
R/W
0
6
INT6
R/W
0
5
INT5
R/W
0
4
INT4
R/W
0
3
INT3
R/W
0
2
INT2
R/W
0
1
INT1
R/W
0
0
INT0
R/W
0
Bits 7:0 – INTF7:0: External Interrupt Flags 7 - 0
When an edge or logic change on the INT7:0 pin triggers an interrupt request, INTF7:0
becomes set (one). If the I-bit in SREG and the corresponding interrupt enable bit, INT7:0 in
EIMSK, are set (one), the MCU will jump to the interrupt vector. The flag is cleared when
the interrupt routine is executed. Alternatively, the flag can be cleared by writing a logical
one to it. These flags are always cleared when INT7:0 are configured as level interrupt. Note
that when entering sleep mode with the INT3:0 interrupts disabled, the input buffers on these
pins will be disabled. This may cause a logic change in internal signals which will set the
INTF3:0 flags. See “Digital Input Enable and Sleep Modes” on page 74 of the
ATMEGA2560 datasheet for more information.
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4.1.2 Functions for configuring interrupt pins (called inside the “port_init()” function)
//Function to configure INT4 (PORTE 4) pin as input for the left position encoder
void left_encoder_pin_config (void)
{
DDRE = DDRE & 0xEF; //Set the direction of the PORTE 4 pin as input
PORTE = PORTE | 0x10; //Enable internal pull-up for PORTE 4 pin
}
//Function to configure INT5 (PORTE 5) pin as input for the right position encoder
void right_encoder_pin_config (void)
{
DDRE = DDRE & 0xDF; //Set the direction of the PORTE 4 pin as input
PORTE = PORTE | 0x20; //Enable internal pull-up for PORTE 4 pin
}
4.1.3 Functions for configuring external interrupts for position encoders
void left_position_encoder_interrupt_init (void) //Interrupt 4 enable
{
cli(); //Clears the global interrupt
EICRB = EICRB | 0x02; // INT4 is set to trigger with falling edge
EIMSK = EIMSK | 0x10; // Enable Interrupt INT4 for left position encoder
sei(); // Enables the global interrupt
}
void right_position_encoder_interrupt_init (void) //Interrupt 5 enable
{
cli(); //Clears the global interrupt
EICRB = EICRB | 0x08; // INT5 is set to trigger with falling edge
EIMSK = EIMSK | 0x20; // Enable Interrupt INT5 for right position encoder
sei(); // Enables the global interrupt
}
4.1.4 Function for initialization of interrupts
//Function to initialize all the devices
void init_devices()
{
cli(); //Clears the global interrupt
left_position_encoder_interrupt_init();
right_position_encoder_interrupt_init();
sei(); // Enables the global interrupt
}
4.1.5 Interrupt Service Routine (ISR)
After initializing interrupts, the next step is to define the Interrupt Service Routine (ISR). ISR in
AVR Studio can be written in two different ways.
a. ISR (INT0_vect)
b. SIGNAL(SIG_INTERRUPT0)
Both of these formats are valid syntactically but we will be using ISR (INT0_vect)
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Various syntaxes for ISR are described in datasheet of ATMEGA2560 microcontroller and also
in < iomxx0_1.h> files in winavr/avr/include/avr folder.
//ISR for right position encoder
ISR(INT5_vect)
{
//Your code
}
//SR for left position encoder
ISR(INT4_vect)
{
//Your code
}
4.2 Robot position control using interrupts
Interrupt 4 (INT4) and interrupt 5 (INT5) are connected to the robot’s position encoder. Position
encoders give position / velocity feedback to the robot. It is used in closed loop to control robot’s
position and velocity. Position encoder consists of optical encoder and slotted disc assembly.
When this slotted disc moves in between the optical encoder we get square wave signal whose
pulse count indicates position and time period indicates velocity. For more details on the
hardware refer to section 3.8 and 3.9 from the Hardware Manual.
Figure 4.1: DC geared motors and position encoders
Figure 4.2: Position encoder assembly
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4.2.1 Calculation of position encoder resolution:
Case 1: Robot is moving forward or backward (encoder resolution is in mm)
Wheel diameter: 5.1cm
Wheel circumference: 5.1cm * 3.14 = 16.014cm = 160.14mm
Number slots on the encoder disc: 30
Position encoder resolution: 163.2 mm / 30 = 5.44mm / pulse.
Case 2: Robot is turning with one wheel rotating clockwise while other wheel is rotating
anti clockwise. Center of rotation is in the center of line passing through wheel axel and
both wheels are rotating in opposite direction (encoder resolution is in degrees)
Distance between Wheels = 15cm
Radius of Circle formed in 3600 rotation of Robot = Distance between Wheels / 2
= 7.5 cm
Distance Covered by Robot in 3600 Rotation = Circumference of Circle traced
= 2 x 7.5 x 3.14
= 47.1 cm or 471mm
Number of wheel rotations of in 3600 rotation of robot
= Circumference of Traced Circle / Circumference of Wheel
= 471 / 160.14
= 2.941
Total pulses in 3600 Rotation of Robot
= Number of slots on the encoder disc / Number of wheel rotations of in 3600 rotation of robot
= 30 x 2.941
= 88.23 (approximately 88)
Position Encoder Resolution in Degrees = 360 / 88
= 4.090 degrees per count
Case 3: Robot is turning with one wheel stationary while other wheel is rotating clockwise
or anti clockwise. Center of rotation is center of the stationary wheel (encoder resolution is
in degrees)
In this case only one wheel is rotating and other wheel is stationary so robot will complete its
3600 rotation with stationary wheel as its center.
Radius of Circle formed in 3600 rotation of Robot = Distance between Wheels
= 15 cm
Distance Covered by Robot in 3600 Rotation = Circumference of Circle traced
= 2 x 15 x 3.14
= 94.20 cm or 942 mm
Number of wheel rotations of in 3600 rotation of robot
= Circumference of Traced Circle / Circumference of Wheel
= 942 / 160.14
= 5.882
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Total pulses in 3600 Rotation of Robot
= Number of slots on the encoder disc / Number of wheel rotations of in 3600 rotation of robot
= 30 x 5.882
= 176.46 (approximately 176)
Position Encoder Resolution in Degrees = 360 /176
= 2.045 degrees per count
4.2.2 Interrupt service routine for position encoder
4.2.2.1 ISR for right position encoder
//ISR for right position encoder
ISR(INT5_vect)
{
ShaftCountRight++; //increment right shaft position count
}
4.2.2.2 ISR for left position encoder
//ISR for left position encoder
ISR(INT4_vect)
{
ShaftCountLeft++; //increment left shaft position count
}
4.2.3 Functions for robot position control
4.2.3.1 Function for rotating robot by specific degrees
//Function used for turning robot by specified degrees
void angle_rotate(unsigned int Degrees)
{
float ReqdShaftCount = 0;
unsigned long int ReqdShaftCountInt = 0;
ReqdShaftCount = (float) Degrees/ 4.090; // division by resolution to get shaft count
ReqdShaftCountInt = (unsigned int) ReqdShaftCount;
ShaftCountRight = 0;
ShaftCountLeft = 0;
while (1)
{
if((ShaftCountRight >= ReqdShaftCountInt) | (ShaftCountLeft >= ReqdShaftCountInt))
break;
}
stop(); //Stop robot
}
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4.2.3.2 Function for moving robot forward and back by specific distance
//Function used for moving robot forward by specified distance
void linear_distance_mm(unsigned int DistanceInMM)
{
float ReqdShaftCount = 0;
unsigned long int ReqdShaftCountInt = 0;
ReqdShaftCount = DistanceInMM / 5.338; // division by resolution to get shaft count
ReqdShaftCountInt = (unsigned long int) ReqdShaftCount;
ShaftCountRight = 0;
while(1)
{
if(ShaftCountRight > ReqdShaftCountInt)
{
break;
}
}
stop(); //Stop robot
}
4.2.3.3 Forward in mm
void forward_mm(unsigned int DistanceInMM)
{
forward();
linear_distance_mm(DistanceInMM);
}
4.2.3.4 Backward in mm
void back_mm(unsigned int DistanceInMM)
{
back();
linear_distance_mm(DistanceInMM);
}
4.2.3.5 left in degrees
void left_degrees(unsigned int Degrees)
{
// 88 pulses for 360 degrees rotation 4.090 degrees per count
left(); //Turn left
angle_rotate(Degrees);
}
4.2.3.6 right in degrees
void right_degrees(unsigned int Degrees)
{
// 88 pulses for 360 degrees rotation 4.090 degrees per count
right(); //Turn right
angle_rotate(Degrees);
}
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4.2.3.7 soft left in degrees
void soft_left_degrees(unsigned int Degrees)
{
// 176 pulses for 360 degrees rotation 2.045 degrees per count
soft_left(); //Turn soft left
Degrees=Degrees*2;
angle_rotate(Degrees);
}
4.2.3.8 soft right in degrees
void soft_right_degrees(unsigned int Degrees)
{
// 176 pulses for 360 degrees rotation 2.045 degrees per count
soft_right(); //Turn soft right
Degrees=Degrees*2;
angle_rotate(Degrees);
}
4.2.3.9 soft left 2 in degrees
void soft_left_2_degrees(unsigned int Degrees)
{
// 176 pulses for 360 degrees rotation 2.045 degrees per count
soft_left_2(); //Turn reverse soft left
Degrees=Degrees*2;
angle_rotate(Degrees);
}
4.2.3.10 soft right 2 in degrees
void soft_right_2_degrees(unsigned int Degrees)
{
// 176 pulses for 360 degrees rotation 2.045 degrees per count
soft_right_2(); //Turn reverse soft right
Degrees=Degrees*2;
angle_rotate(Degrees);
}
4.2.4 Application example of robot position control
Located in the folder “Experiments \ Position_Control_Interrupts” folder in the documentation
CD.
This experiment demonstrates use of position encoders.
Concepts covered: External Interrupts, Position control
Connections:
PORTA3 to PORTA0: Robot direction control
PL3, PL4: Robot velocity control. Currently set to 1 as PWM is not used
PE4 (INT4): External interrupt for left motor position encoder
PE5 (INT5): External interrupt for the right position encoder
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Note:
1. Make sure that in the configuration options following settings are done for proper operation of
the code
Microcontroller: ATMEGA2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
It is observed that external interrupts does not work with the optimization level -Os
2. Auxiliary power can supply current up to 1 Ampere while Battery can supply current up to 2
Ampere. When both motors of the robot changes direction suddenly without stopping, it
produces large current surge. When robot is powered by Auxiliary power which can supply only
1 Ampere of current, sudden direction change in both the motors will cause current surge which
can reset the microcontroller because of sudden fall in voltage. It is a good practice to stop the
motors for at least 0.5seconds before changing the direction. This will also increase the useable
time of the fully charged battery.
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5. Timer / Counter Operations on the Robot
ATMEGA2560 has 2 eight bit timers (timer 0 and timer 2) and 4 sixteen bit timers (timer 1, 3, 4
and 5). All the timers have independent Output Compare Units with PWM support. These timers
can be used for accurate program execution timing (event management) and wave generation.
Fire Bird V uses these timers mainly for the following applications:
•
•
•
•
Velocity control – Timer 5 is used to generate PWM for robot’s velocity control.
Servo motor control – Timer 1 is used in 10 bit fast PWM mode to control servo motors.
Event scheduling – Timer with timer overflow interrupt is used for event scheduling.
Velocity calculation – Timer can be used for robot’s velocity estimation.
In the Fire Bird V ATMEGA2560 robot Timer 5 is used to generate PWM for robot velocity
control. Timer 1 is used for servo motor control. All other timers are free and can be used for
other purposes.
Note: Theory content of this chapter is based on the ATMEGA2560 datasheet which is located
in the “datasheet” folder in the documentation CD.
General features of the 8 bit timers 0 and 2
• Two Independent Output Compare Units
• Double Buffered Output Compare Registers
• Clear Timer on Compare Match (Auto Reload)
• Glitch Free, Phase Correct Pulse Width Modulator (PWM)
• Variable PWM Period
• Frequency Generator
• Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)
General features of the 16 bit timers 1, 3, 4 and 5
• True 16-bit Design (i.e., Allows 16-bit PWM)
• Three independent Output Compare Units
• Double Buffered Output Compare Registers
• One Input Capture Unit
• Input Capture Noise Canceler
• Clear Timer on Compare Match (Auto Reload)
• Glitch-free, Phase Correct Pulse Width Modulator (PWM)
• Variable PWM Period
• Frequency Generator
• External Event Counter
• Twenty independent interrupt sources (TOV1, OCF1A, OCF1B, OCF1C, ICF1, TOV3,
OCF3A, OCF3B, OCF3C, ICF3, TOV4, OCF4A, OCF4B, OCF4C, ICF4, TOV5,
OCF5A, OCF5B, OCF5C and ICF5)
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5.1 Important terms involved in the timers:
BOTTOM: The counter reaches the BOTTOM when it becomes 0x0000.
MAX: The counter reaches its MAX value when it becomes 0xFF (decimal 255) for 8 bit timer
or 0xFFFF (decimal 65535) for 16 bit timer.
TOP: The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be one of the fixed values: 0x00FF, 0x01FF, or
0x03FF, or to the value stored in the OCRnA or ICRn Register. The assignment is dependent on
the mode of operation.
Accessing 16-bit Registers
The TCNTn, OCRnA/B/C, and ICRn are 16-bit registers that can be accessed by the AVR CPU
via the 8-bit data bus. The 16-bit register must be byte accessed using two read or write
operations. Each 16-bit timer has a single 8-bit register for temporary storing of the high byte of
the 16-bit access. The same Temporary Register is shared between all 16-bit registers within
each 16-bit timer. Accessing the low byte triggers the 16-bit read or write operation. When the
low byte of a 16-bit register is written by the CPU, the high byte stored in the Temporary
Register, and the low byte written are both copied into the 16-bit register in the same clock cycle.
When the low byte of a 16-bit register is read by the CPU, the high byte of the 16-bit register is
copied into the Temporary Register in the same clock cycle as the low byte is read.
Not all 16-bit accesses uses the Temporary Register for the high byte. Reading the OCRnA/B/C
16-bit registers does not involve using the Temporary Register. To do a 16-bit write, the high
byte must be written before the low byte. For a 16-bit read, the low byte must be read before the
high byte.
Modes of operation in timers:
1. Normal mode
2. Clear timer on compare match (CTC) mode
3. Fast PWM mode
4. Phase correct PWM mode
5. Phase and frequency correct PWM mode
For more information on the timer operation refer to ATMEGA2560 datasheet.
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5.2 16 bit Timer Registers
Note:
• In all the terms ‘n’ represents timer number which can be 1, 3, 4 or 5 and ‘X’ represents
output compare channel number which can be A, B or C.
• For more detailed description refer to section 16 to section 20 of the ATMEGA2560
datasheet which is located in the “datasheet” folder in the documentation CD.
Clock source for the Timers
The Timer/Counter can be clocked by an internal or an external clock source. The clock source is
selected by the Clock Select logic which is controlled by the Clock Select CSn2:0) bits located in
the Timer/Counter control Register B (TCCRnB). Timer/Counter 0, 1, 3, 4, and 5 share the same
prescaler module, but the Timer/Counters can have different prescaler settings. The description
below applies to all Timer/Counters. Tn is used as a general name, n = 1, 3, 4 or 5.
The Timer/Counter can be clocked directly by the system clock (by setting the CSn2:0 = 1). This
provides the fastest operation, with a maximum Timer/Counter clock frequency equal to system
clock frequency (fCLK_I/O). Alternatively, one of four taps from the prescaler can be used as a
clock source. The prescaled clock has a frequency of either fCLK_I/O/8, fCLK_I/O/64,
fCLK_I/O/256, or fCLK_I/O/1024.
5.2.1 TCCRnA – Timer/Counter Control Register A
Bit
Read / Write
Initial Value
7
COMnA1
R/W
0
6
COMnA0
R/W
0
5
COMnB1
R/W
0
4
COMnB0
R/W
0
3
COMnC1
R/W
0
2
COMnC0
R/W
0
1
WGMn1
R/W
0
0
WGMn0
R/W
0
Bit 7:6 – COMnA1:0: Compare Output Mode for Channel A
Bit 5:4 – COMnB1:0: Compare Output Mode for Channel B
Bit 3:2 – COMnC1:0: Compare Output Mode for Channel C
The COMnA1:0, COMnB1:0, and COMnC1:0 control the output compare pins (OCnA, OCnB,
and OCnC respectively) behavior. If one or both of the COMnA1:0 bits are written to one, the
OCnA output overrides the normal port functionality of the I/O pin it is connected to. If one or
both of the COMnB1:0 bits are written to one, the OCnB output overrides the normal port
functionality of the I/O pin it is connected to. If one or both of the COMnC1:0 bits are written to
one, the OCnC output overrides the normal port functionality of the I/O pin it is connected to.
However, note that the Data Direction Register (DDR) bit corresponding to the OCnA, OCnB or
OCnC pin must be set in order to enable the output driver. When the OCnA, OCnB or OCnC is
connected to the pin, the function of the COMnX1:0 bits is dependent of the WGMn3:0 bits
setting. Table 5.1 shows the COMnA1:0, COMnB1:0 and COMnC1:0 bit functionality when the
WGMn3:0 bits are set to the fast PWM mode.
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COMnA1
COMnB1
COMnC1
0
0
COMnA0
COMnB0
COMnC0
0
1
1
0
1
1
Description
Normal port operation, OC5A, OCnB, OCnC disconnected
WGMn3:0 = 14 or 15: Toggle OCnA on Compare Match, OCnB and OCnC
disconnected (normal port operation). For all other WGMn settings, normal
port operation, OCnA/OCnB/OCnC disconnected.
Clear OCnA/OCnB/OCnC on compare match, set OCnA/OCnB/OCnC at
BOTTOM (non-inverting mode).
Set OCnA/OCnB/OCnC on compare match, clear OCnA/OCnB/OCnC at
BOTTOM (inverting mode).
Table 5.1: COMnX1:0 bit functionality when the WGMn3:0 bits are set to fast PWM
mode.
Bit 1:0 – WGM51:0: Waveform Generation Mode
Combined with the WGMn3:2 bits found in the TCCRnB Register, these bits control the
counting sequence of the counter, the source for maximum (TOP) counter value, and what type
of waveform generation to be used, see Table 5.3. Modes of operation supported by the
Timer/Counter unit are: Normal mode (counter), Clear Timer on Compare match (CTC) mode,
and three types of Pulse Width Modulation (PWM) modes. For more information on the different
modes, refer “Modes of Operation” on page 148 of the ATMEGA2560 datasheet.
5.2.2 TCCRnB – Timer/Counter Control Register B
Bit
Read / Write
Initial Value
7
ICNCn
R/W
0
6
ICESn
R/W
0
5
R
0
4
WGMn3
R/W
0
3
WGMn2
R/W
0
2
CSn2
R/W
0
1
CSn1
R/W
0
0
CSn0
R/W
0
Bit 7 – ICNC5: Input Capture Noise Canceler
Setting this bit (to one) activates the Input Capture Noise Canceler. When the Noise Canceler is
activated, the input from the Input Capture Pin (ICPn) is filtered. The filter function requires four
successive equal valued samples of the ICPn pin for changing its output. The input capture is
therefore delayed by four Oscillator cycles when the noise canceler is enabled.
Bit 6 – ICESn: Input Capture Edge Select
This bit selects which edge on the Input Capture Pin (ICP5) that is used to trigger a capture
event. When the ICES5 bit is written to zero, a falling (negative) edge is used as trigger, and
when the ICESn bit is written to one, a rising (positive) edge will trigger the capture. When a
capture is triggered according to the ICESn setting, the counter value is copied into the Input
Capture Register (ICRn). The event will also set the Input Capture Flag (ICFn), and this can be
used to cause an Input Capture Interrupt, if this interrupt is enabled. When the ICRn is used as
TOP value (see description of the WGMn3:0 bits located in the TCCRnA and the TCCRnB
Register), the ICPn is disconnected and consequently the input capture function is disabled.
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Bit 5 – Reserved Bit
This bit is reserved for future use. For ensuring compatibility with future devices, this bit must be
written to zero when TCCRnB is written.
Bit 4:3 – WGMn3:2: Waveform Generation Mode
See TCCRnA Register description and refer to table 5.3
Bit 2:0 – CSn2:0: Clock Select
The three clock select bits select the clock source to be used by the Timer/Counter.
CSn2
0
0
0
0
1
1
1
1
CSn1
0
0
1
1
0
0
1
1
CSn0
0
1
0
1
0
1
0
1
Description
No clock source. (Timer/Counter stopped)
clkI/O/1 (No prescaling)
clkI/O/8 (From prescaler)
clkI/O/64 (From prescaler)
clkI/O/256 (From prescaler)
clkI/O/1024 (From prescaler)
External clock source on Tn pin. Clock on falling edge
External clock source on Tn pin. Clock on rising edge
Table 5.2: Clock select bit description
5.2.3 TCCRnC – Timer/Counter Control Register C
Bit
Read / Write
Initial Value
7
FOCnA
W
0
6
FOCnB
W
0
5
FOCnC
W
0
4
R
0
3
R
0
2
R
0
1
R
0
0
R
0
Bit 7 – FOCnA: Force Output Compare for Channel A
Bit 6 – FOCnB: Force Output Compare for Channel B
Bit 5 – FOCnC: Force Output Compare for Channel C
The FOCnA/FOCnB/FOCnC bits are only active when the WGMn3:0 bits specifies a non-PWM
mode. When writing a logical one to the FOCnA/FOCnB/FOCnC bit, an immediate compare
match is forced on the waveform generation unit. The OCnA/OCnB/OCnC output is changed
according to its COMnX1:0 bits setting. Note that the FOCnA/FOCnB/FOCnC bits are
implemented as strobes. Therefore it is the value present in the COMnx1:0 bits that determine
the effect of the forced compare. A FOCnA/FOCnB/FOCnC strobe will not generate any
interrupt nor will it clear the timer in Clear Timer on Compare Match (CTC) mode using
OCRnA as TOP. The FOCnA/FOCnB/FOCnB bits are always read as zero.
Bit 4:0 – Reserved Bits
These bits are reserved for future use. For ensuring compatibility with future devices, these bits
must be written to zero when TCCRnC is written.
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Table 5.3: Waveform generation mode bit description
5.2.4 TIMSKn – Timer/Counter n Interrupt Mask Register
Bit
Read / Write
Initial Value
7
R
0
6
R
0
5
ICIEn
R/W
0
4
R
0
3
OCIEnC
R/W
0
2
OCIEnB
R/W
0
1
OCIEnA
R/W
0
0
TOIEn
R/W
0
Bit 5 – ICIEn: Timer/Counter n, Input Capture Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter n Input Capture interrupt is enabled. The corresponding Interrupt
Vector (See “Interrupts” on page 105 in the ATMEGA2560 datasheet.) is executed when the
ICFn Flag, located in TIFRn, is set.
Bit 3 – OCIEnC: Timer/Counter n, Output Compare C Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter n Output Compare C Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 105 in the ATMEGA2560 datasheet.) is executed
when the OCFnC Flag, located in TIFRn, is set.
Bit 2 – OCIEnB: Timer/Counter n, Output Compare B Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter n Output Compare B Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 105 in the ATMEGA2560 datasheet.) is executed
when the OCFnB Flag, located in TIFRn, is set.
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Bit 1 – OCIEnA: Timer/Counter n, Output Compare A Match Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter n Output Compare A Match interrupt is enabled. The corresponding
Interrupt Vector (See “Interrupts” on page 105 in the ATMEGA2560 datasheet.) is executed
when the OCFnA Flag, located in TIFRn, is set.
Bit 0 – TOIEn: Timer/Counter n, Overflow Interrupt Enable
When this bit is written to one, and the I-flag in the Status Register is set (interrupts globally
enabled), the Timer/Counter n Overflow interrupt is enabled. The corresponding Interrupt Vector
(See “Interrupts” on page 105 in the ATMEGA2560 datasheet.) is executed when the TOVn
Flag, located in TIFRn, is set.
5.2.5 TIFRn – Timer/Counter n Interrupt Flag Register
Bit
Read / Write
Initial Value
7
R
0
6
R
0
5
ICFn
R/W
0
4
R
0
3
OCFnC
R/W
0
2
OCFnB
R/W
0
1
OCFnA
R/W
0
0
TOVn
R/W
0
Bit 5 – ICFn: Timer/Counter n, Input Capture Flag
This flag is set when a capture event occurs on the ICPn pin. When the Input Capture Register
(ICRn) is set by the WGMn3:0 to be used as the TOP value, the ICFn Flag is set when the
counter reaches the TOP value. ICFn is automatically cleared when the Input Capture Interrupt
Vector is executed. Alternatively, ICFn can be cleared by writing a logic one to its bit location.
Bit 3– OCFnC: Timer/Counter n, Output Compare C Match Flag
This flag is set in the timer clock cycle after the counter (TCNTn) value matches the Output
Compare Register C (OCRnC). Note that a Forced Output Compare (FOCnC) strobe will not set
the OCFnC Flag. OCFnC is automatically cleared when the Output Compare Match C Interrupt
Vector is executed. Alternatively, OCFnC can be cleared by writing a logic one to its bit
location.
Bit 2 – OCFnB: Timer/Counter1, Output Compare B Match Flag
This flag is set in the timer clock cycle after the counter (TCNTn) value matches the Output
Compare Register B (OCRnB). Note that a Forced Output Compare (FOCnB) strobe will not set
the OCFnB Flag. OCFnB is automatically cleared when the Output Compare Match B Interrupt
Vector is executed. Alternatively, OCFnB can be cleared by writing a logic one to its bit
location.
Bit 1 – OCF1A: Timer/Counter1, Output Compare A Match Flag
This flag is set in the timer clock cycle after the counter (TCNTn value matches the Output
Compare Register A (OCRnA). Note that a Forced Output Compare (FOCnA) strobe will not set
the OCFnA Flag. OCFnA is automatically cleared when the Output Compare Match A Interrupt
Vector is executed. Alternatively, OCFnA can be cleared by writing a logic one to its bit
location.
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Bit 0 – TOVn: Timer/Counter n, Overflow Flag
The setting of this flag is dependent of the WGMn3:0 bits setting. In Normal and CTC modes,
the TOVn Flag is set when the timer overflows. Refer to Table 5.3 for the TOVn Flag behavior
when using another WGMn3:0 bit setting. TOVn is automatically cleared when the
Timer/Counter n Overflow Interrupt Vector is executed. Alternatively, TOVn can be cleared by
writing a logic one to its bit location.
5.3 Velocity control using PWM
5.3.1 Concept of PWM
Pulse width modulation is a process in which duty cycle of constant frequency square wave is
modulated to control power delivered to the load i.e. motor.
Duty cycle is the ratio of ‘T-ON/ T’. Where ‘T-ON’ is ON time and ‘T’ is the time period of the
wave. Power delivered to the motor is proportional to the ‘T-ON’ time of the signal. In case of
PWM the motor reacts to the time average of the signal.
PWM is used to control total amount of power delivered to the load without power losses which
generally occur in resistive methods of power control.
Figure 5.1: Pulse Width Modulation (PWM)
Above figure shows the PWM waveforms for motor velocity control. In case (A), ON time is
90% of time period. This wave has more average value. Hence more power is delivered to the
motor. In case (B), the motor will run slower as the ON time is just 10% of time period.
Microcontroller Pin
PL3 (OC5A)
PL4 (OC5B)
PA0
PA1
PA2
PA3
Function
Pulse width modulation for the left motor (velocity control)
Pulse width modulation for the right motor (velocity control)
Left motor direction control
Left motor direction control
Right motor direction control
Right motor direction control
Table 5.4: Pin functions for the motion control
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5.3.2 PWM generation using Timer
PWM using Timer n
All 16 bit timers are identical in nature. We are using timer 5 for PWM as input pins of the motor
driver IC L293D are connected to PL3 (OC5A) and PL4 (OC5B).
For robot velocity control Timer 5 is used in 8 bit fast PWM generation mode. In the non
inverting compare output mode.
The counter counts from BOTTOM to MAX and again restarts from BOTTOM. In non-inverting
compare output mode, the output compare (OC5X) is cleared on the compare match between
TCNT5 and OCR5X, and set at BOTTOM. Where X is A, B or C. In inverting compare output
mode output (OC5X) is set on compare match and cleared at BOTTOM.
Figure 5.2: Time diagram for fast PWM mode
In 8 bit fast PWM mode the counter is incremented until the counter value matches either fixed
value of 0x00FF hex and then value is rolled over again to 0. In the non-inverting PWM mode
output on the output compare pins (OC5A, OC5B and OC5C in this case) is logic 0 when
counter starts at 0. When counter value is matched with OCRnx (in this case OCR5AL,
OCR5BL and OCR5CL output at the output at the corresponding compare pins (OC5A, OC5B
and OC5C in this case) becomes logic 1. It stays at logic 1 till counter rolls over from 0xFF to 0.
At the roll over value of these OCRnx pins is set to logic 0. To change the duty cycle of the
PWM form 0 to 100% duty cycle in the 8 bit fast PWM generation mode value of OCRnx can be
set between 0 to 255 (0x00 to 0xFF).
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5.3.3 Timer 5 configuration in 8 bit fast PWM mode
Function Timer5_init() function initializes the function in 8 bit fast PWM generation mode.
// Timer 5 initialized in PWM mode for velocity control
// Prescale: 256
// PWM 8bit fast, TOP=0x00FF
// Timer Frequency:225.000Hz
void timer5_init()
{
TCCR5B = 0x00;
//Stop
TCNT5H = 0xFF;
//Counter higher 8-bit value to which OCR5xH value is compared with
TCNT5L = 0x01;
//Counter lower 8-bit value to which OCR5xH value is compared with
OCR5AH = 0x00;
//Output compare register high value for Left Motor
OCR5AL = 0xFF;
//Output compare register low value for Left Motor
OCR5BH = 0x00;
//Output compare register high value for Right Motor
OCR5BL = 0xFF;
//Output compare register low value for Right Motor
OCR5CH = 0x00;
//Output compare register high value for Motor C1
OCR5CL = 0xFF;
//Output compare register low value for Motor C1
TCCR5A = 0xA9;
//COM5A1=1, COM5A0=0; COM5B1=1, COM5B0=0; COM5C1=1
// COM5C0=0
//For Overriding normal port functionality to OCRnA outputs. WGM51=0, WGM50=1 Along With GM52 //in
TCCR5B for Selecting FAST PWM 8-bit Mode
TCCR5B = 0x0B;
//WGM12=1; CS12=0, CS11=1, CS10=1 (Prescaler=64)
}
PWM frequency calculation:
PWM frequency = System Clock / N (1 + TOP)
= 14.7456 MHz / 256 (1 + 255)
= 225.000 Hz
Where
System clock = Crystal frequency = 14.7456MHz
Prescale = N = 256
TOP = 255 (8 bit resolution)
System Clock / Prescale
System Clock
System Clock / 8
System Clock / 64
System Clock / 256
System Clock / 1024
8-bit (TOP = 255)
Fpwm = 57.600 KHz
Fpwm = 7.200 KHz
Fpwm = 900.000Hz
Fpwm = 225.000 Hz
Fpwm = 56.250 Hz
Table 5.2: 8 bit PWM fast frequency for different prescale options
5.3.4 Function for timer 5 initialization
void init_devices (void) //use this function to initialize all devices
{
cli(); //disable all interrupts
timer5_init();
sei(); //re-enable interrupts
}
cli(); disables all the interrupts and sei(); enables all the interrupts.
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It is very important that all the devices should be configured after disabling all the interrupts. All
the peripherals of the microcontroller will be configured inside init_devices() function.
5.3.5 Functions for PWM output pin configuration and robot’s velocity control
5.3.5.1 Functions for PWM output pin configuration (called inside the “port_init()”
function)
void motion_pin_config (void)
{
DDRA = DDRA | 0x0F;
PORTA = PORTA & 0xF0;
DDRL = DDRL | 0x18; //Setting PL3 and PL4 pins as output for PWM generation
PORTL = PORTL | 0x18; //PL3 and PL4 pins are for velocity control using PWM.
}
5.3.5.2 Function for robot’s velocity control
void velocity (unsigned char left_motor, unsigned char right_motor)
{
OCR5AL = (unsigned char)left_motor;
OCR5BL = (unsigned char)right_motor;
}
This function takes velocity for left motor and right motor as input parameter and assigns them to
output compare register OCR5A and OCR5B. Channel A is used for left motor and channel B is
used for right motor. Since we are using PWM in 8 bit resolution its ok to only loading lower
byte of the OCR5A and OCR5B registers.
5.3.6 Application example for robot velocity control
Located in the folder “Experiments \ Velocity_Control_using_PWM” folder in the
documentation CD.
This experiment demonstrates robot velocity control using PWM.
Concepts covered: Use of timer to generate PWM for velocity control
There are two components to the motion control:
1. Direction control using pins PORTA0 to PORTA3
2. Velocity control by PWM on pins PL3 and PL4 using OC5A and OC5B of timer 5.
Connections: Refer to table 5.1 for connection details.
Note:
1. Make sure that in the configuration options following settings are done for proper operation of
the code
Microcontroller: ATMEGA2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
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2. Auxiliary power can supply current up to 1 Ampere while Battery can supply current up to 2
Ampere. When both motors of the robot changes direction suddenly without stopping, it
produces large current surge. When robot is powered by Auxiliary power which can supply only
1 Ampere of current, sudden direction change in both the motors will cause current surge which
can reset the microcontroller because of sudden fall in voltage. It is a good practice to stop the
motors for at least 0.5seconds before changing the direction. This will also increase the useable
time of the fully charged battery.
5.4 Servo motor control using Timer 1
Fire Bird V robot has camera pod and sensor pod attachment. It has two servo motor for pan and
tilt movement. Servo motor is an essentially geared DC motor which rotates from 00 to 1800
based upon input signal in the form of pulse train.
Servo control is done by sending a PWM signal to the PWM input pin of the servo motor. The
servo motor compares this signal to the actual position of the servo and adjusts the angle of the
servo motor accordingly. Position of the servo motor is determined by the pulse width of
waveform which has frequency between 30Hz to 60Hz. Generic servo motor gives 0 to 180
degrees rotation for pulse width of 1 to 2 milliseconds. 50Hz is considered as ideal frequency.
The pulse width may change for different type of servo motor
We will be generating approximately 52.25 Hz (approx 19.13ms time period) PWM signal using
timer 1. Pulse will remain high for first 1 to 2 ms depending on the angle we want to set and then
pulse will remain low for the rest of the time.
Camera pod has two servo motors called as pan and tilt motors. Pan motor moves camera left
and right. It has 1800 swing. Tilt motor moves camera up and down. It can also give swing of
1800 but after mounting camera swing gets restricted to 0 to 1200.
We will control these servo motors using timer 1. Very high resolution PWM waveform can be
generated using timer input capture or overflow interrupt along with output compare register
(OCR) but it is bit complicated method and requires frequent interrupt servicing. We will be
using a simpler method to generate control signal for these servo motors which gives relatively
less resolution in servo angle control but does not require frequent interrupt servicing. Timer 1
will be used in 10 bit fast PWM mode which has 10 bit resolution. Servo motor can be connected
to the three servo connectors (S1, S2 and S3) which are located on the ATMEGA2560
microcontroller adaptor board. For more details refer to section 3.19.11 from the Hardware
Manual.
For concept of PWM and PWM generation using timer refer to section 5.3.1 and 5.3.2.
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5.4.1 Timer 1 configuration in 10 bit fast PWM mode
Function Timer1_init() function initializes the function in 10 bit fast PWM generation mode.
//TIMER1 initialization in 10 bit fast PWM mode
//prescale:256
// WGM: 7) PWM 10bit fast, TOP=0x03FF
// actual value: 52.25Hz
void timer1_init(void)
{
TCCR1B = 0x00;
//stop
TCNT1H = 0xFC;
//Counter high value to which OCR1xH value is to be compared with
TCNT1L = 0x01;
//Counter low value to which OCR1xH value is to be compared with
OCR1AH = 0x03;
//Output compare Register high value for servo 1
OCR1AL = 0xFF;
//Output Compare Register low Value For servo 1
OCR1BH = 0x03;
//Output compare Register high value for servo 2
OCR1BL = 0xFF;
//Output Compare Register low Value For servo 2
OCR1CH = 0x03;
//Output compare Register high value for servo 3
OCR1CL = 0xFF;
//Output Compare Register low Value For servo 3
ICR1H = 0x03;
ICR1L = 0xFF;
TCCR1A = 0xAB;
//COM1A1=1, COM1A0=0; COM1B1=1, COM1B0=0; COM1C1=1 COM1C0=0
//For Overriding normal port functionality to OCRnA outputs. WGM11=1, WGM10=1. Along With //WGM12 in
TCCR1B for Selecting FAST PWM Mode TCCR1C = 0x00;
TCCR1B = 0x0C; //WGM12=1; CS12=1, CS11=0, CS10=0 (Prescaler=256)
}
5.4.2 Timer 1 initialization
//Function to initialize all the peripherals
void init_devices(void)
{
cli(); //disable all interrupts
port_init();
timer1_init();
sei(); //re-enable interrupts
}
5.4.3 Functions to rotate servo motor by specified angle in the multiple of 1.86 degrees
//Function to rotate Servo 1 by a specified angle in the multiples of 1.86 degrees
void servo_1(unsigned char degrees)
{
float PositionPanServo = 0;
PositionPanServo = ((float)degrees / 1.86) + 35.0;
OCR1AH = 0x00;
OCR1AL = (unsigned char) PositionPanServo;
}
//Function to rotate Servo 2 by a specified angle in the multiples of 1.86 degrees
void servo_2(unsigned char degrees)
{
float PositionTiltServo = 0;
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PositionTiltServo = ((float)degrees / 1.86) + 35.0;
OCR1BH = 0x00;
OCR1BL = (unsigned char) PositionTiltServo;
}
//Function to rotate Servo 3 by a specified angle in the multiples of 1.86 degrees
void servo_3(unsigned char degrees)
{
float PositionServo = 0;
PositionServo = ((float)degrees / 1.86) + 35.0;
OCR1CH = 0x00;
OCR1CL = (unsigned char) PositionServo;
}
5.4.4 Functions to make servo motor free to rotate
"servo_n_free” functions unlock the servo motors from the any angle and make them free by
giving 100% duty cycle at the PWM. This function can be used to reduce the power consumption
of the motor if it is holding any load against the gravity.
void servo_1_free (void) //makes servo 1 free rotating
{
OCR1AH = 0x03;
OCR1AL = 0xFF; //Servo 1 off
}
void servo_2_free (void) //makes servo 2 free rotating
{
OCR1BH = 0x03;
OCR1BL = 0xFF; //Servo 2 off
}
void servo_3_free (void) //makes servo 3 free rotating
{
OCR1CH = 0x03;
OCR1CL = 0xFF; //Servo 3 off
}
5.4.5 Application example for servo motor control
Located in the folder “Experiments \ Servo_Motor_Control_using_PWM” folder in the
documentation CD.
This experiment demonstrates Servo motor control using 10 bit fast PWM mode.
Concepts covered: Use of timer to generate PWM for servo motor control
Connection Details:
PORTB 5 (OC1A): Servo 1(Camera pod pan servo)
PORTB 6 (OC1B): Servo 2 (Camera pod tile servo)
PORTB 7 (OC1C): Servo 3 (Reserved)
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Note:
1. Make sure that in the configuration options following settings are done for proper operation of
the code
Microcontroller: ATMEGA2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
2. 5V supply to these motors is provided by separate low drop voltage regulator "5V Servo"
which can supply maximum of 800mA current. It is a good practice to move one servo at a time
to reduce power surge in the robot's supply lines. Also preferably take ADC readings while servo
motor is not moving or stopped moving after giving desired position.
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6. LCD Interfacing
To interface LCD with the microcontroller in default configuration requires 3 control signals and
8 data lines. This is known as 8 bit interfacing mode which requires total 11 I/O lines. To reduce
the number of I/Os required for LCD interfacing we can use 4 bit interfacing mode which
requires 3 control signals with 4 data lines. In this mode upper nibble and lower nibble of
commands/data set needs to be sent separately. Figure 6.1 shows LCD interfacing in 4 bit mode.
The three control lines are referred to as EN, RS, and RW.
Figure 6.1: LCD interfacing in 4 bit mode
Microcontroller
VCC
GND
PC0
PC1
PC2
PC4 to PC7
LCD PINS
VCC
GND
RS (Control line)
R/W (Control line)
EN (Control Line)
D4 to D7 (Data lines)
LED+, LED-
Description
Supply voltage (5V).
Ground
Register Select
READ /WRITE
Enable
Bidirectional Data Bus
Backlight control
Table 6.1: LCD pin mapping with the microcontroller
The EN line is called "Enable" and it is connected to PC2. This control line is used to tell the
LCD that microcontroller has sent data to it or microcontroller is ready to receive data from
LCD. This is indicated by a high-to-low transition on this line. To send data to the LCD, program
should make sure that this line is low (0) and then set the other two control lines as required and
put data on the data bus. When this is done, make EN high (1) and wait for the minimum amount
of time as specified by the LCD datasheet, and end by bringing it to low (0) again.
The RS line is the "Register Select" line and it is connected to PC0. When RS is low (0), the data
is treated as a command or special instruction by the LCD (such as clear screen, position cursor,
etc.). When RS is high (1), the data being sent is treated as text data which should be displayed
on the screen.
The RW line is the "Read/Write" control line and it is connected to PC1. When RW is low (0),
the information on the data bus is being written to the LCD. When RW is high (1), the program
is effectively querying (or reading from) the LCD.
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The data bus is bidirectional, 4 bit wide and is connected to PC4 to PC7 of the microcontroller.
The MSB bit (DB7) of data bus is also used as a Busy flag. When the Busy flag is 1, the LCD is
in internal operation mode, and the next instruction will not be accepted. When RS = 0 and R/W
= 1, the Busy flag is output on DB7. The next instruction must be written after ensuring that the
busy flag is 0.
We are using LCD in 4-bit mode. In the 4-bit mode the data is sent in nibbles with higher nibble
sent first followed by the lower nibble. Initialization of LCD in 4-bit mode is done only after
setting the LCD for 4-bit mode. LCD reset sequence include following steps.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Wait for about 20ms.
Send the first value 0x30.
Wait for about 10ms.
Send the second value 0x30.
Wait for about 1ms.
Send the third value 0x30.
Wait for about 1ms.
Send 0x20 for selecting 4-bit mode.
Wait for 1ms.
Before we can display any data on the LCD we need to initialize the LCD for proper operation.
The first instruction we send must tell the LCD that we will be communicating with it using 4-bit
data bus. Remember that the RS line must be low if we are sending a command to the LCD. In
the second and third instruction we clear and reset the display of the LCD. The fourth instruction
sets the display and cursor ON. In fifth instruction we place the cursor at the start. Check the
lcd_init( ) function to see how all this is put in code.
The function lcd_reset() and lcd_init completes the initialization of LCD in 4-bit mode. Now
following steps are followed to send the command/data in 4-bit mode.
1.
2.
3.
4.
5.
6.
7.
Mask lower 4-bits.
Send command/data to the LCD port.
Send enable signal to EN pin.
Mask higher 4-bits.
Shift bits left by 4 positions (to bring lower bits to upper bits position).
Send command/data to the LCD port.
Send enable signal to EN pin.
The function lcd_wr_command() and lcd_wr_char() are for sending the command and data
respectively to the LCD.
For using the busy flag (polling method) the LCD is read in the similar way, i.e. nibble by nibble,
here we are not using the polling method and instead we are providing the necessary delay
between the commands.
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After the initialization of LCD in 4-bit mode is complete, then for sending the data in nibbles
there is no need of providing any delay between two nibbles of same byte, the most significant
nibble (higher 4-bits) is sent first, immediately followed by the least significant nibble (lower 4bits).
Figure 6.2: LCD interface timing diagram
For more details on the LCD, refer to “hd44780u.pdf” in the folder “datasheet” in the
documentation CD.
6.1 Functions used for the LCD display
Note: All the functions are defined in the lcd.c file. It is located inside the “Experiments” folder
inside the documentation CD.
6.1.1 LCD port configure (called inside the “port_init()” function)
void lcd_port_config (void)
{
DDRC = DDRC | 0xF7; //all the LCD pin's direction set as output
PORTC = PORTC & 0x80; // all the LCD pins are set to logic 0 except PORTC 7
}
6.1.2 Setting LCD in 4 bit mode
void lcd_set_4bit()
{
_delay_ms(1);
cbit(lcd_port,RS);
cbit(lcd_port,RW);
lcd_port = 0x30;
sbit(lcd_port,EN);
_delay_ms(5);
cbit(lcd_port,EN);
//RS=0 --- Command Input
//RW=0 --- Writing to LCD
//Sending 3 in the upper nibble
//Set Enable Pin
//delay
//Clear Enable Pin
_delay_ms(1);
cbit(lcd_port,RS);
cbit(lcd_port,RW);
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//RS=0 --- Command Input
//RW=0 --- Writing to LCD
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lcd_port = 0x30;
sbit(lcd_port,EN);
_delay_ms(5);
cbit(lcd_port,EN);
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//Sending 3 in the upper nibble
//Set Enable Pin
//delay
//Clear Enable Pin
_delay_ms(1);
cbit(lcd_port,RS);
cbit(lcd_port,RW);
lcd_port = 0x30;
sbit(lcd_port,EN);
_delay_ms(5);
cbit(lcd_port,EN);
//RS=0 --- Command Input
//RW=0 --- Writing to LCD
//Sending 3 in the upper nibble
//Set Enable Pin
//delay
//Clear Enable Pin
_delay_ms(1);
cbit(lcd_port,RS);
cbit(lcd_port,RW);
lcd_port = 0x20;
sbit(lcd_port,EN);
_delay_ms(5);
cbit(lcd_port,EN);
//RS=0 --- Command Input
//RW=0 --- Writing to LCD
//Sending 2 in the upper nibble to initialize LCD 4-bit mode
//Set Enable Pin
//delay
//Clear Enable Pin
}
6.1.3 LCD initialization function
//Function to Initialize LCD
void lcd_init()
{
_delay_ms(1);
lcd_wr_command(0x28);
lcd_wr_command(0x01);
lcd_wr_command(0x06);
lcd_wr_command(0x0E);
lcd_wr_command(0x80);
}
//4-bit mode and 5x8 dot character font
//Clear LCD display
//Auto increment cursor position
//Turn on LCD and cursor
//Set cursor position
6.1.4 Function to write command on LCD
//Function to write command on LCD
void lcd_wr_command(unsigned char cmd)
{
unsigned char temp;
temp = cmd;
temp = temp & 0xF0;
lcd_port &= 0x0F;
lcd_port |= temp;
cbit(lcd_port,RS);
cbit(lcd_port,RW);
sbit(lcd_port,EN);
_delay_ms(5);
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cbit(lcd_port,EN);
cmd = cmd & 0x0F;
cmd = cmd<<4;
lcd_port &= 0x0F;
lcd_port |= cmd;
cbit(lcd_port,RS);
cbit(lcd_port,RW);
sbit(lcd_port,EN);
_delay_ms(5);
cbit(lcd_port,EN);
}
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6.1.4 Function to write data on LCD
cbit(lcd_port,EN);
//Function to write data on LCD
void lcd_wr_char(char letter)
{
char temp;
temp = letter;
temp = (temp & 0xF0);
lcd_port &= 0x0F;
lcd_port |= temp;
sbit(lcd_port,RS);
cbit(lcd_port,RW);
sbit(lcd_port,EN);
_delay_ms(5);
letter = letter & 0x0F;
letter = letter<<4;
lcd_port &= 0x0F;
lcd_port |= letter;
sbit(lcd_port,RS);
cbit(lcd_port,RW);
sbit(lcd_port,EN);
_delay_ms(5);
cbit(lcd_port,EN);
}
6.1.5 Function for LCD home
void lcd_home()
{
lcd_wr_command(0x80);
}
6.1.6 Function to Print String on LCD
void lcd_string(char *str)
{
while(*str != '\0')
{
lcd_wr_char(*str);
str++;
}
}
6.1.7 Position the LCD cursor at "row", "column"
//Position the LCD cursor at "row", "column"
void lcd_cursor (char row, char column)
{
switch (row) {
case 1: lcd_wr_command (0x80 + column - 1); break;
case 2: lcd_wr_command (0xc0 + column - 1); break;
case 3: lcd_wr_command (0x94 + column - 1); break;
case 4: lcd_wr_command (0xd4 + column - 1); break;
default: break;
}
}
6.1.8 Function to print any input value up to the desired digit on LCD
// Function to print any input value up to the
desired digit on LCD
void lcd_print (char row, char column, unsigned
int value, int digits)
{
unsigned char flag=0;
if(row==0||coloumn==0)
{
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lcd_home();
}
else
{
lcd_cursor (row, column);
}
if(digits==5 || flag==1)
{
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if(digits==2 || flag==1)
{
temp = value/10;
tens = temp%10 + 48;
lcd_wr_char(tens);
flag=1;
}
if(digits==1 || flag==1)
{
unit = value%10 + 48;
lcd_wr_char(unit);
}
if(digits>5)
{
lcd_wr_char('E');
}
million=value/10000+48;
lcd_wr_char(million);
flag=1;
}
if(digits==4 || flag==1)
{
temp = value/1000;
thousand = temp%10 + 48;
lcd_wr_char(thousand);
flag=1;
}
if(digits==3 || flag==1)
{
temp = value/100;
hundred = temp%10 + 48;
lcd_wr_char(hundred);
flag=1;
}
}
6.2 Application examples
6.2.1 Application example to print string on the LCD
Located in the folder “Experiments \ LCD_interfcing” folder in the documentation CD.
This program shows how to write string on the LCD
Note:
1. Make sure that in the configuration options following settings are done for proper operation of
the code
Microcontroller: ATMEGA2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
2. Buzzer is connected to PC3. Hence to operate buzzer without interfering with the LCD,
buzzer should be turned on or off only using buzzer function
6.2.2 Application example to print sensor data on the LCD
It also involves concept of ADC. It will be covered in chapter 7.
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7. Analog to Digital Conversion
Fire Bird V has three white line sensors, one Sharp IR range sensor with four add-on sockets for
additional Sharp IR range sensors, eight Analog IR proximity sensors. Robot can also measure
its own battery voltage and current. All these sensors give analog output. We need to use
ATMEGA2560 microcontroller's ADC (Analog to Digital Converter) to convert these analog
values in to digital values.
The ATMEGA2560 features a 10-bit successive approximation Analog to Digital Converter
(ADC). The ADC block is connected to an 16-channel Analog Multiplexer which allows 16
single-ended voltage inputs from the pins of PORTF and PORTK. The minimum value
represents GND and the maximum value represents the voltage on the AREF pin (5 Volt in the
case of Fire Bird V).
7.1 ADC Resolution
The resolution of the ADC indicates the number of discrete values it can produce over the range
of analog values. The values are usually stored electronically in binary form, so the resolution is
usually expressed in bits. In consequence, the number of discrete values available, or "levels", is
usually a power of two. For example, an ADC with a resolution of 8 bits can encode an analog
input to one in 256 different levels, since 28 = 256. The values can represent the ranges from 0 to
255 (i.e. unsigned integer) or from -128 to 127 (i.e. signed integer), depending on the
application.
ATMEGA2560 microcontroller has ADC with 10 bit resolution.
V resolution = V full scale / 2n – 1
Where V full scale = 5V; n = 10 or 8
Case 1: n = 10 (10 bit resolution)
V resolution = 5V / 210 -1
V resolution = 4.8875mV
Case 2: n = 8 (8 bit resolution)
V resolution = 5V / 28 -1
V resolution = 19.6078mV
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7.2 Registers for ADC
7.2.1 ADCSRA – ADC Control and Status Register A
Bit
Read / Write
Initial Value
7
ADEN
R/W
0
6
ADSC
R/W
0
5
ADATE
R/W
0
4
ADIF
R/W
0
3
ADIE
R/W
0
2
ADPS2
R/W
0
1
ADPS1
R/W
0
0
ADPS0
R/W
0
Bit 7 – ADEN: ADC Enable
Writing this bit to one enables the ADC. By writing it to zero, the ADC is turned off. Turning off
the ADC while a conversion is in progress, will terminate this conversion.
Bit 6 – ADSC: ADC Start Conversion
In Single Conversion mode, write this bit to one to start each conversion. In Free Running mode,
write this bit to one to start the first conversion. The first conversion after ADSC has been
written after the ADC has been enabled, or if ADSC is written at the same time as the ADC is
enabled, will take 25 ADC clock cycles instead of the normal 13. This first conversion performs
initialization of the ADC. ADSC will read as one as long as a conversion is in progress. When
the conversion is complete, it returns to zero. Writing zero to this bit has no effect.
Bit 5 – ADATE: ADC Auto Trigger Enable
When this bit is written to one, Auto Triggering of the ADC is enabled. The ADC will start a
conversion on a positive edge of the selected trigger signal. The trigger source is selected by
setting the ADC Trigger Select bits, ADTS in ADCSRB.
Bit 4 – ADIF: ADC Interrupt Flag
This bit is set when an ADC conversion completes and the Data Registers are updated. The ADC
Conversion Complete Interrupt is executed if the ADIE bit and the I-bit in SREG are set. ADIF
is cleared by hardware when executing the corresponding interrupt handling vector.
Alternatively, ADIF is cleared by writing a logical one to the flag. Beware that if doing a ReadModify-Write on ADCSRA, a pending interrupt can be disabled. This also applies if the SBI and
CBI instructions are used.
Bit 3 – ADIE: ADC Interrupt Enable
When this bit is written to one and the I-bit in SREG is set, the ADC Conversion Complete
Interrupt is activated.
Bits 2:0 – ADPS2:0: ADC Prescaler Select Bits
These bits determine the division factor between the XTAL frequency and the input clock to the
ADC.
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ADPS2
0
0
0
0
1
1
1
1
ADPS1
0
0
1
1
0
0
1
1
ADPS0
0
1
0
1
0
1
0
1
Division Factor
2
2
4
8
16
32
64
128
Table 7.1 ADC prescaler selections
7.2.2 ADCSRB – ADC Control and Status Register B
Bit
7
R
0
Read / Write
Initial Value
6
ACME
R/W
0
5
R
0
4
R
0
3
MUX5
R/W
0
2
ADTS2
R/W
0
1
ADTS1
R/W
0
0
ADTS0
R/W
0
Bit 3 – MUX5: Analog Channel and Gain Selection Bit
This bit is used together with MUX4:0 in ADMUX to select which combination in of analog
inputs are connected to the ADC. If this bit is changed during a conversion, the change will not
go in effect until this conversion is complete. For more details refer to table 26.4 in the
ATMEGA2560 datasheet.
7.2.3 ADMUX– ADC Multiplexer Selection Register
Bit
Read / Write
Initial Value
7
REFS1
R/W
0
6
REFS0
R/W
0
5
ADLAR
R/W
0
4
MUX4
R/W
0
3
MUX3
R/W
0
2
MUX2
R/W
0
1
MUX1
R/W
0
0
MUX0
R/W
0
Bit 7:6 – REFS1:0: Reference Selection Bits
As shown in Table 7.2, these bits select the voltage reference for the ADC. If these bits are
changed during a conversion, the change will not go in effect until this conversion is complete
(ADIF in ADCSRA is set). The internal voltage reference options may not be used if an external
reference voltage is being applied to the AREF pin.
REFS1
0
0
1
1
REFS0
0
1
0
1
Voltage Reference Selection
AREF, Internal VREF turned off
AVCC with external capacitor at AREF pin
Internal 1.1V Voltage Reference with external capacitor at AREF pin
Internal 2.56V Voltage Reference with external capacitor at AREF pin
Table 7.2: Voltage reference selection for ADC
Note:
If 10x or 200x gain is selected, only 2.56 V should be used as Internal Voltage Reference. For
differential conversion, only 1.1V cannot be used as internal voltage reference.
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Bit 5 – ADLAR: ADC Left Adjust Result
The ADLAR bit affects the presentation of the ADC conversion result in the ADC Data Register.
Write one to ADLAR to left adjust the result. Otherwise, the result is right adjusted. Changing
the ADLAR bit will affect the ADC Data Register immediately, regardless of any ongoing
conversions. For a complete description of this bit, see “ADCL and ADCH – The ADC Data
Register” in the section 7.2.5.
Bits 4:0 – MUX4:0: Analog Channel and Gain Selection Bits
The value of these bits selects which combination of analog inputs are connected to the ADC.
For more details see Table 7.3. If these bits are changed during a conversion, the change will not
go in effect until this conversion is complete (ADIF in ADCSRA is set)
MUX5:0
000000
000001
000010
000011
000100
000101
000110
000111
100000
100001
100010
100011
100100
100101
100110
100111
ADC pin
PF0/ADC0
PF1/ADC1
PF2/ADC2
PF3/ADC3
PF4/ADC4/TCK
PF5(ADC5/TMS)
PF6/(ADC6/TD0)
PF7(ADC7/TDI)
PK0/ADC8/PCINT16
PK1/ADC9/PCINT17
PK2/ADC10/PCINT18
PK3/ADC11/PCINT19
PK4/ADC12/PCINT20
PK5/ADC13/PCINT21
PK6/ADC14/PCINT22
PK7/ADC15/PCINT23
Pin function
ADC input for battery voltage monitoring
ADC input for white line sensor 3
ADC input for white line sensor 2
ADC input for white line sensor 1
ADC input for IR proximity analog sensor 1*****
ADC input for IR proximity analog sensor 2*****
ADC input for IR proximity analog sensor 3*****
ADC input for IR proximity analog sensor 4*****
ADC input for IR proximity analog sensor 5
ADC input for Sharp IR range sensor 1
ADC input for Sharp IR range sensor 2
ADC input for Sharp IR range sensor 3
ADC input for Sharp IR range sensor 4
ADC input for Sharp IR range sensor 5
ADC Input For Servo Pod 1
ADC Input For Servo Pod 2
Pin status
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Input (Floating)
Table 7.3 Input channel selection and functions
***** For using Analog IR proximity (1, 2, 3 and 4) sensors short the jumper J2. To use JTAG
via expansion slot of the microcontroller socket remove these jumpers.
Note:
Table 7.3 is a simplified version of the table 26.4 from the ATMEGA2560 datasheet customized
to the Fire Bird V ATMEGA2560 robot
MUX4:1 are located inside ADMUX register. MUX5 is located in the ADCSRB register.
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7.2.4 ACSR – Analog Comparator Control and Status Register
Bit
Read / Write
Initial Value
7
ACD
R/W
0
6
ACBG
R/W
0
5
ACO
R
0
4
ACI
R/W
0
3
ACIE
R/W
0
2
ACIC
R/W
0
1
ACIS1
R/W
0
0
ACIS0
R/W
0
Bit 7 – ACD: Analog Comparator Disable
When this bit is written logic one, the power to the Analog Comparator is switched off. This bit
can be set at any time to turn off the Analog Comparator. This will reduce power consumption in
Active and Idle mode. When changing the ACD bit, the Analog Comparator Interrupt must be
disabled by clearing the ACIE bit in ACSR. Otherwise an interrupt can occur when the bit is
changed.
Bit 6 – ACBG: Analog Comparator Bandgap Select
When this bit is set, a fixed bandgap reference voltage replaces the positive input to the Analog
Comparator. When this bit is cleared, AIN0 is applied to the positive input of the Analog
Comparator. When the bandgap reference is used as input to the Analog Comparator, it will take
a certain time for the voltage to stabilize. If not stabilized, the first conversion may give a wrong
value. For more information see “Internal Voltage Reference” on page 62 of the ATMEGA2560
datasheet.
Bit 5 – ACO: Analog Comparator Output
The output of the Analog Comparator is synchronized and then directly connected to ACO. The
synchronization introduces a delay of 1 - 2 clock cycles.
Bit 4 – ACI: Analog Comparator Interrupt Flag
This bit is set by hardware when a comparator output event triggers the interrupt mode defined
by ACIS1 and ACIS0. The Analog Comparator interrupt routine is executed if the ACIE bit is
set and the I-bit in SREG is set. ACI is cleared by hardware when executing the corresponding
interrupt handling vector. Alternatively, ACI is cleared by writing a logic one to the flag.
Bit 3 – ACIE: Analog Comparator Interrupt Enable
When the ACIE bit is written logic one and the I-bit in the Status Register is set, the Analog
Comparator interrupt is activated. When written logic zero, the interrupt is disabled.
Bit 2 – ACIC: Analog Comparator Input Capture Enable
When written logic one, this bit enables the input capture function in Timer/Counter1 to be
triggered by the Analog Comparator. The comparator output is in this case directly connected to
the input capture front-end logic, making the comparator utilize the noise canceler and edge
select features of the Timer/Counter1 Input Capture interrupt. When written logic zero, no
connection between the Analog Comparator and the input capture function exists. To make the
comparator trigger the Timer/Counter1 Input Capture interrupt, the ICIE1 bit in the Timer
Interrupt Mask Register (TIMSK1) must be set.
Bits 1, 0 – ACIS1, ACIS0: Analog Comparator Interrupt Mode Select
These bits determine which comparator events that trigger the Analog Comparator interrupt. The
different settings are shown in Table 7.4.
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ACIS1
0
0
1
1
ACIS0
0
1
0
1
Interrupt mode
Comparator Interrupt on Output Toggle
Reserved
Comparator Interrupt on Falling Output Edge
Comparator Interrupt on Rising Output Edge
Table 7.4: ACIS1/ACIS0 settings
7.2.5 ADCL and ADCH – The ADC Data Register
Case 1: ADLAR = 0;
Initial value
Read / Write
Bit
ADCH
ADCL
Bit
Read / Write
Initial value
0
R
15
0
R
14
0
R
13
0
R
12
0
R
11
0
R
10
ADC2
2
R
0
0
R
9
ADC9
ADC1
1
R
0
0
R
8
ADC8
ADC0
0
R
0
ADC7
7
R
0
ADC6
6
R
0
ADC5
5
R
0
ADC4
4
R
0
ADC3
3
R
0
0
R
13
ADC7
0
R
12
ADC6
0
R
11
ADC5
0
R
10
ADC4
0
R
9
ADC3
0
R
8
ADC2
5
R
0
4
R
0
3
R
0
2
R
0
1
R
0
0
R
0
Case 2: ADLAR = 1; (Left adjust)
Initial value
Read / Write
Bit
ADCH
ADCL
Bit
Read / Write
Initial value
0
R
15
ADC9
ADC1
7
R
0
0
R
14
ADC8
ADC0
6
R
0
When an ADC conversion is complete, the result is found in these two registers. If differential
channels are used, the result is presented in two’s complement form. When ADCL is read, the
ADC Data Register is not updated until ADCH is read. Consequently, if the result is left adjusted
and no more than 8-bit precision (7 bit + sign bit for differential input channels) is required, it is
sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH. The ADLAR bit in
ADMUX, and the MUXn bits in ADMUX affect the way the result is read from the registers. If
ADLAR is set, the result is left adjusted. If ADLAR is cleared (default), the result is right
adjusted.
7.3 Functions for ADC
7.3.1 Function to configure pins for ADC (called inside the “port_init()” function)
//ADC pin configuration
void adc_pin_config (void)
{
DDRF = 0x00; //set PORTF direction as input
PORTF = 0x00; //set PORTF pins floating
DDRK = 0x00; //set PORTK direction as input
PORTK = 0x00; //set PORTK pins floating
}
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7.3.2 Function to configure ADC
//Function to Initialize ADC
void adc_init()
{
ADCSRA = 0x00;
ADCSRB = 0x00;
ADMUX = 0x20;
ACSR = 0x80;
ADCSRA = 0x86;
}
//MUX5 = 0
//Vref=5V external --- ADLAR=1 --- MUX4:0 = 0000
//ADEN=1 --- ADIE=1 --- ADPS2:0 = 1 1 0
7.3.3 Function to initialize ADC
void init_devices (void)
{
cli(); //Clears the global interrupts
port_init();
adc_init();
sei(); //Enables the global interrupts
}
7.3.4 Function to get ADC value
//This Function accepts the Channel Number and returns the corresponding Analog Value
unsigned char ADC_Conversion(unsigned char Ch)
{
unsigned char a;
if(Ch>7)
{
ADCSRB = 0x08;
}
Ch = Ch & 0x07;
ADMUX= 0x20| Ch;
ADCSRA = ADCSRA | 0x40;
//Set start conversion bit
while((ADCSRA&0x10)==0);
//Wait for ADC conversion to complete
a=ADCH;
ADCSRA = ADCSRA|0x10;
//clear ADIF (ADC Interrupt Flag) by writing 1 to it
ADCSRB = 0x00;
return a;
}
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7.4 Application examples
7.4.1 Application example to display ADC sensor data on the LCD
Located in the folder “Experiments \ ADC_Sensor_Display_on_LCD” folder in the
documentation CD.
7.4.2 Application example to follow white line
Located in the folder “Experiments \ White_Line_Following” folder in the documentation CD.
7.4.3 Application example to perform Adaptive Cruise Control (ACC) while following the
white line
Located in the folder “Experiments \ Adaptive_Cruise_Control” folder in the documentation CD.
Note for all the application examples:
Note:
1. Make sure that in the configuration options following settings are done for proper operation of
the code
Microcontroller: ATMEGA2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
2. Make sure that you copy the lcd.c file in your folder
3. Distance calculation is for Sharp GP2D12 (10cm-80cm) IR Range sensor
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8. Serial Communication
Serial Communication using UART
The Fire Bird V can communicate with other robots / devices serially using either wired link or
wireless module. Serial communication is done in asynchronous mode. In the asynchronous
mode, the common clock signal is not required at both the transmitter and receiver for data
synchronization.
ATMEGA2560 have four USART (0 to 3) ports available for serial communication.
1. RS232 Serial Communication on UART1.
2. USB Communication using FT232 USB to serial converter on UART2.
3. ZigBee Wireless Communication on UART0 (if XBee wireless module is installed).
4. TTL level serial communication pins on the expansion port on the microcontroller
adaptor board by UART3.
8.1 Registers involved in the serial communication
Note: in the following registers ‘n’ represents the UART number which can be 0, 1, 2 or 3.
8.1.1 UCSRnA – USART Control and Status Register A
Bit
Read / Write
Initial Value
7
RXCn
R
0
6
TXCn
R/W
0
5
UDREn
R
0
4
FEn
R
0
3
DORn
R
0
2
UPEn
R
0
1
U2Xn
R/W
0
0
MPCMn
R/W
0
Bit 7 – RXCn: USART Receive Complete
This flag bit is set when there are unread data in the receive buffer and cleared when the receive
buffer is empty (i.e., does not contain any unread data). If the Receiver is disabled, the receive
buffer will be flushed and consequently the RXCn bit will become zero. The RXCn Flag can be
used to generate a Receive Complete interrupt (see description of the RXCIEn bit in the section
8.1.2).
Bit 6 – TXCn: USART Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted out and
there are no new data currently present in the transmit buffer (UDRn). The TXCn Flag bit is
automatically cleared when a transmit complete interrupt is executed, or it can be cleared by
writing a one to its bit location. The TXCn Flag can generate a Transmit Complete interrupt (see
description of the TXCIEn bit in the section 8.1.2 in the ATMEGA2560 datasheet).
Bit 5 – UDREn: USART Data Register Empty
The UDREn Flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREn
is one, the buffer is empty, and therefore ready to be written. The UDREn Flag can generate a
Data Register Empty interrupt (see description of the UDRIEn bit). UDREn is set after a reset to
indicate that the Transmitter is ready.
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Bit 4 – FEn: Frame Error
This bit is set if the next character in the receive buffer had a Frame Error when received. I.E.
when the first stop bit of the next character in the receive buffer is zero. This bit is valid until the
receive buffer (UDRn) is read. The FEn bit is zero when the stop bit of received data is one.
Always set this bit to zero when writing to UCSRnA.
Bit 3 – DORn: Data OverRun
This bit is set if a Data OverRun condition is detected. A Data OverRun occurs when the receive
buffer is full (two characters), it is a new character waiting in the Receive Shift Register, and a
new start bit is detected. This bit is valid until the receive buffer (UDRn) is read. Always set this
bit to zero when writing to UCSRnA.
Bit 2 – UPEn: USART Parity Error
This bit is set if the next character in the receive buffer had a Parity Error when received and the
Parity Checking was enabled at that point (UPMn1 = 1). This bit is valid until the receive buffer
(UDRn) is read. Always set this bit to zero when writing to UCSRnA.
Bit 1 – U2Xn: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using
synchronous operation. Writing this bit to one will reduce the divisor of the baud rate divider
from 16 to 8 effectively doubling the transfer rate for asynchronous communication.
Bit 0 – MPCMn: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCMn bit is written to
one, all the incoming frames received by the USART Receiver that do not contain address
information will be ignored. The Transmitter is unaffected by the MPCMn setting. For more
detailed information see “Multi-processor Communication Mode” on page 222 of the
ATMEGA2560 datasheet.
8.1.2 UCSRnB – USART Control and Status Register n B
Bit
Read / Write
Initial Value
7
RXCIEn
R/W
0
6
TXCIEn
R/W
0
5
UDRIEn
R/W
0
4
RXENn
R/W
0
3
TXENn
R/W
0
2
UCSZn2
R/W
0
1
RXB8n
R
0
0
TXB8n
R/W
0
Bit 7 – RXCIEn: RX Complete Interrupt Enable n
Writing this bit to one enables interrupt on the RXCn Flag. A USART Receive Complete
interrupt will be generated only if the RXCIEn bit is written to one, the Global Interrupt Flag in
SREG is written to one and the RXCn bit in UCSRnA is set.
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Bit 6 – TXCIEn: TX Complete Interrupt Enable n
Writing this bit to one enables interrupt on the TXCn Flag. A USART Transmit Complete
interrupt will be generated only if the TXCIEn bit is written to one, the Global Interrupt Flag in
SREG is written to one and the TXCn bit in UCSRnA is set.
Bit 5 – UDRIEn: USART Data Register Empty Interrupt Enable n
Writing this bit to one enables interrupt on the UDREn Flag. A Data Register Empty interrupt
will be generated only if the UDRIEn bit is written to one, the Global Interrupt Flag in SREG is
written to one and the UDREn bit in UCSRnA is set.
Bit 4 – RXENn: Receiver Enable n
Writing this bit to one enables the USART Receiver. The Receiver will override normal port
operation for the RxDn pin when enabled. Disabling the Receiver will flush the receive buffer
invalidating the FEn, DORn, and UPEn Flags.
Bit 3 – TXENn: Transmitter Enable n
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal
port operation for the TxDn pin when enabled. The disabling of the Transmitter (writing TXENn
to zero) will not become effective until ongoing and pending transmissions are completed, i.e.,
when the Transmit Shift Register and Transmit Buffer Register do not contain data to be
transmitted. When disabled, the Transmitter will no longer override the TxDn port.
Bit 2 – UCSZn2: Character Size n
The UCSZn2 bits combined with the UCSZn1:0 bit in UCSRnC sets the number of data bits
(Character Size) in a frame the Receiver and Transmitter use.
Bit 1 – RXB8n: Receive Data Bit 8 n
RXB8n is the ninth data bit of the received character when operating with serial frames with nine
data bits. Must be read before reading the low bits from UDRn.
Bit 0 – TXB8n: Transmit Data Bit 8 n
TXB8n is the ninth data bit in the character to be transmitted when operating with serial frames
with nine data bits. Must be written before writing the low bits to UDRn.
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8.1.3 UCSRnC – USART Control and Status Register n C
Bit
Read / Write
Initial Value
7
UMSELn1
R/W
0
6
UMSELn0
R/W
0
5
UPMn1
R/W
0
4
UPMn0
R/W
0
3
USBSn
R/W
0
2
UCSZn1
R/W
0
1
UCSZn0
R/W
0
0
UCP0Ln
R/W
0
Bits 7:6 – UMSELn1:0 USART Mode Select
These bits select the mode of operation of the USARTn as shown in Table 8.1.
UMSELn1
0
0
1
1
UMSELn0
0
1
0
1
Mode
Asynchronous USART
Synchronous USART
(Reserved)
Master SPI (MSPIM)(1)
Table 8.1: UMSELn Bit settings
Note: See “USART in SPI Mode” on page 232 of the ATMEGA2560 datasheet for full
description of the Master SPI Mode (MSPIM) operation
Bits 5:4 – UPMn1:0: Parity Mode
These bits enable and set type of parity generation and check. If enabled, the Transmitter will
automatically generate and send the parity of the transmitted data bits within each frame. The
Receiver will generate a parity value for the incoming data and compare it to the UPMn setting.
If a mismatch is detected, the UPEn Flag in UCSRnA will be set.
UPMn1
0
0
1
1
UPMn0
0
1
0
1
Parity mode
Disabled
Reserved
Enabled, Even Parity
Enabled, Odd Parity
Table 8.2: UPMn Bits settings
Bit 3 – USBSn: Stop Bit Select
This bit selects the number of stop bits to be inserted by the Transmitter. The Receiver ignores
this setting.
USBSn
0
1
Stop Bit(s)
1-bit
2-bit
Table 8.3: USBSbit settings
Bit 2:1 – UCSZn1:0: Character Size
The UCSZn1:0 bits combined with the UCSZn2 bit in UCSRnB sets the number of data bits
(Character Size) in a frame the Receiver and Transmitter use.
UCSZn2
0
0
0
0
1
1
1
1
UCSZn1
0
0
1
1
0
0
1
1
UCSZn0
0
1
0
1
0
1
0
1
Character size
5-bit
6-bit
7-bit
8-bit
Reserved
Reserved
Reserved
9-bit
Table 8.4: UCSZn Bits Settings
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Bit 0 – UCPOLn: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous mode is
used. The UCPOLn bit sets the relationship between data output change and data input sample,
and the synchronous clock (XCKn).
UCPOLn
0
1
Transmitted Data Changed (Output
of TxDn Pin)
Rising XCKn Edge
Falling XCKn Edge
Received Data Sampled (Input on
RxDn Pin)
Falling XCKn Edge
Rising XCKn Edge
Table 8.5: UCPOLn Bit Settings
8.1.4 UBRRnL and UBRRnH – USART Baud Rate Registers
Initial value
Read / Write
Bit
ADCH
ADCL
Bit
Read / Write
Initial value
0
R
15
UBRR7
7
R/W
0
0
R
14
UBRR6
6
R/W
0
0
R
13
UBRR5
5
R/W
0
0
R
12
UBRR4
4
R/W
0
0
R/W
11
UBRR11
UBRR3
3
R/W
0
0
R/W
10
UBRR10
UBRR2
2
R/W
0
0
R/W
9
UBRR9
UBRR1
1
R/W
0
0
R/W
8
UBRR8
UBRR0
0
R/W
0
Baud rate calculation:
Crystal frequency: 14.7456 MHz
Required baud rate: 9600 bits per second
UBRR = (System Clock / (16 * baud rate)) – 1
= (14.7456 MHz / (16 * 9600)) – 1
= 95
= 0x5F (hex)
UBRRH = 0x00
UBRRL = 0x5F
Baud rate 2400 4800 9600 14.4k 19.2k 28.8k 38.4k 57.6k 76.8k 115.2k
Table 8.6: Value of UBRR for different baud rate for 14.7456 MHz crystal
For 14.7456MHz crystal frequency, the most commonly used baud rates for asynchronous
operation can be generated by using the UBRR settings as shown in the table 8.6.
Note:
While loading values in the UBRR register load values in the UBRRH resistor first and then in
UBRRL register.
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8.1.5 UDRn – USART I/O Data Register n
The USART Transmit Data Buffer Register and USART Receive Data Buffer Registers share
the same I/O address referred to as USART Data Register or UDRn. The Transmit Data Buffer
Register (TXB) will be the destination for data written to the UDRn Register location. Reading
the UDRn Register location will return the contents of the Receive Data Buffer Register (RXB).
For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the Transmitter and set to
zero by the Receiver.
The transmit buffer can only be written when the UDREn Flag in the UCSRnA Register is set.
Data written to UDRn when the UDREn Flag is not set, will be ignored by the USART
Transmitter. When data is written to the transmit buffer, and the Transmitter is enabled, the
Transmitter will load the data into the Transmit Shift Register when the Shift Register is empty.
Then the data will be serially transmitted on the TxDn pin.
The receive buffer consists of a two level FIFO. The FIFO will change its state whenever the
receive buffer is accessed. Due to this behavior of the receive buffer, do not use Read-ModifyWrite instructions (SBI and CBI) on this location. Be careful when using bit test instructions
(SBIC and SBIS), since these also will change the state of the FIFO.
8.2 Functions used in serial communication
Note:
In all the functions below function will remain same for other UARTs. Only ‘1’ of UART1 will
be replaced with the appropriate UART number
8.2.1 Function to configure UART1
//Function To Initialize UART1
// desired baud rate:9600
// actual baud rate:9600 (error 0.0%)
// char size: 8 bit
// parity: Disabled
void uart1_init(void)
{
UCSR1B = 0x00; //disable while setting baud rate
UCSR1A = 0x00;
UCSR1C = 0x06;
UBRR1L = 0x5F; //set baud rate lo
UBRR1H = 0x00; //set baud rate hi
UCSR1B = 0x98;
}
8.2.2 Function to initialize uart 1
void init_devices()
{
cli(); //Clears the global interrupts
port_init(); //Initializes all the ports
uart1_init(); //Initialize UART1 for serial communication
sei(); //Enables the global interrupts
}
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8.2.3 Receive complete ISR
When UART receives eight data bits on receive pin of the microcontroller, RXC flag is set. If
RXCIE interrupt is enabled then receive complete interrupt triggers ISR. This ISR then reads
valid data from UDR1 and stores it in a separate variable before next character is received and
overwritten. It is always recommended to save data read from UDR1 in a separate variable as
next character received will overwrite and destroy the existing data in UDR1.
SIGNAL(SIG_USART1_RECV) // ISR for receive complete interrupt
{
data = UDR1;
//making copy of data from UDR1 in 'data' variable
//Insert your coder here
}
8.2.4 Data register empty ISR
The transmitter side of the UART is double buffered containing UDRn to hold the data written
from the program and transmit register to actually transmit parallel data sequentially bit-by-bit
on the transmit pin. The data written to UDRn is transferred to transmit register. At this point, the
UDRn is available to accept next data word from the program. This sets UDRE flag and if
UDRIE interrupt is enabled then UDRn data register empty interrupt triggers ISR. This ISR then
loads next data byte to be transmitted into UDRn.
SIGNAL (SIG_USART1_DATA)
{
UDR1 = tx_data;
// Insert your code here……….
}
8.2.5 Transmit complete ISR
In the case of packet based data communication it is necessary to know when a byte has been
completely transmitted out of microcontroller. The TXC flag is provided to indicate that the
transmit register is empty and no new data is waiting to be transmitted. If transmit register is
empty it sets TXC flag and if TXCIE interrupt is enabled then Transmit complete interrupt
triggers ISR. This ISR can be used as a confirmation of the byte that was loaded in UDR1 is
successfully transmitted out of the microcontroller transmit pin. This interrupt can be used to
check if all the bytes in a packet transmission are transmitted successfully.
SIGNAL (SIG_USART1_TRANS)
{
//Insert your code here………..
}
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8.3 Application example for serial communication
Note:
All the application examples are identical in nature.
Robot can be controlled using wired or wireless link using PC with these application examples.
Refer to chapter 6 from the Hardware Manual for using these application examples.
8.3.1 RS232 serial communication using UART1
Located in the folder “Experiments \ A_Serial_Communication” folder in the documentation
CD.
8.3.2 USB communication using FT232 USB to serial converter using UART2
Located in the folder “Experiments \ B_Serial_Communication_USB-RS232” folder in the
documentation CD.
8.3.3 Serial communication over wireless using ZigBee wireless module sing UART0
Located in the folder “Experiments \ C_Serial_Communication_ZigBee_wireless” folder in the
documentation CD.
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9. SPI Communication
Fire Bird V robot can be interfaced with more than 30 sensors at the same time. ATMEGA2560
does not have sufficient number of ADC available of sensor interfacing. Hence ATMEGA8
microcontroller is connected with ATMEGA2560 microcontroller over the SPI port. Jumper J4
needs to be removed before attempting to do ISP with ATMEGA2560 and ATMEGA8 as there
SPI lines are connected with the jumper J4. For more details on the jumpers, refer to the section
3.19.6 in the Hardware Manual.
Figure 9.1: SPI Interface Block Diagram
9.1 Concept of SPI communication
The Serial Peripheral Interface (SPI) allows high-speed synchronous data transfer between
several peripheral devices or between microcontrollers. ATMEGA2560 and ATMEGA8 both
have inbuilt SPI peripheral. SPI pins consist of MOSI (Master Output Slave Input), MISO
(Master Input Slave Output), SCK (Serial Clock) and SS* (Slave Select).
Features of the SPI communication:
• Full-duplex, Three-wire Synchronous Data Transfer
• Master or Slave Operation
• LSB First or MSB First Data Transfer
• Seven Programmable Bit Rates
• End of Transmission Interrupt Flag
• Write Collision Flag Protection
• Wake-up from Idle Mode
• Double Speed (CK/2) Master SPI Mode
SPI communication process:
The basic operation of SPI involves the Master initiating the communication.
•
•
Master sets the SS (Slave Select) pin low to tell the slave that communication is about to
start.
The master writes a byte onto MOSI (Master Output Slave Input) pin and the slave does
the same on the MISO (Master Input Slave Output) pin.
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•
As the master ticks the clock pin SCK it will read the value of MISO pin and slave will
read the value of MOSI pin.
Note:
For master any pin can act as slave select while for slave, pin SS must be used as Slave Select.
The communication through SPI interface is a simultaneous transmission and reception through
Shift Registers. The data is exchanged bit by bit serially between the master and slave shift
registers.
Figure 9.2: SPI MASTER-SLAVE Interconnection (Ref: ATMEGA2560 datasheet)
For example SPI master shift register have 0x8E and SPI slave shift register have 0x32 initially,
now as the master initiates the communication by setting the SS pin high. One bit from either of
the shift registers is transferred to other on each clock tick at the SCK pin. Figure 9.3 explains
this process.
Figure 9.3: Byte transfer between master and slave device in SPI communication
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Thus one byte is completely transmitted after eight clock cycles and data byte of slave and
master are exchanged simultaneously. In order to receive a byte from the slave microcontroller,
master microcontroller has to send a byte to the slave microcontroller.
9.2 Registers involved in the SPI communication
9.2.1 SPCR – SPI Control Register
Bit
Read / Write
Initial Value
7
SPIE
R/W
0
6
SPE
R/W
0
5
DORD
R/W
0
4
MSTR
R/W
0
3
CPOL
R/W
0
2
CPHA
R/W
0
1
SPR1
R/W
0
0
SPR0
R/W
0
Bit 7 – SPIE: SPI Interrupt Enable
This bit causes the SPI interrupt to be executed if SPIF bit in the SPSR Register is set and if the
Global Interrupt Enable bit in SREG is set.
Bit 6 – SPE: SPI Enable
When the SPE bit is written to one, the SPI is enabled. This bit must be set to enable any SPI
operations.
Bit 5 – DORD: Data Order
When the DORD bit is written to one, the LSB of the data word is transmitted first. When the
DORD bit is written to zero, the MSB of the data word is transmitted first.
Bit 4 – MSTR: Master/Slave Select
This bit selects Master SPI mode when written to one, and Slave SPI mode when written logic
zero. If SS is configured as an input and is driven low while MSTR is set, MSTR will be cleared,
and SPIF in SPSR will become set. The user will then have to set MSTR to re-enable SPI Master
mode.
Bit 3 – CPOL: Clock Polarity
When this bit is written to one, SCK is high when idle. When CPOL is written to zero, SCK is
low when idle. Refer to figure 9.4 and figure 9.5 for an example. The CPOL functionality is
summarized in the table 9.1.
CPOL
0
1
Leading Edge
Rising
Falling
Trailing Edge
Falling
Rising
Table 9.1: CPOL functionality
Bit 2 – CPHA: Clock Phase
The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading (first) or
trailing (last) edge of SCK. Refer to figure 9.4 and figure 9.5 for an example. The CPOL
functionality is summarized in the table 9.2.
CPHA
0
1
Leading Edge
Sample
Setup
Trailing Edge
Setup
Sample
Table 9.2: CPHA functionality
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Bits 1, 0 – SPR1, SPR0: SPI Clock Rate Select 1 and 0
These two bits control the SCK rate of the device configured as a Master. SPR1 and SPR0 have
no effect on the Slave. The relationship between SCK and the Oscillator Clock frequency fosc is
shown in the table 9.3.
SPI2X
0
0
0
0
1
1
1
1
SPR1
0
0
1
1
0
0
1
1
SPR0
0
1
0
1
0
1
0
1
SCK Frequency
Fosc/4
Fosc/16
Fosc/64
Fosc/128
Fosc/2
Fosc/8
Fosc/32
Fosc/64
Table 9.3: Relationship between SCK and the oscillator frequency
Figure 9.4: SPI transfer format with CPHA = 0
Figure 9.5: SPI transfer format with CPHA = 1
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9.2.2 SPSR – SPI Status Register
Bit
Read / Write
Initial Value
7
SPIF
R
0
6
WCOL
R
0
5
R
0
4
R
0
3
R
0
2
R
0
1
R
0
0
SPI2X
R/W
0
Bit 7 – SPIF: SPI Interrupt Flag
When a serial transfer is complete, the SPIF Flag is set. An interrupt is generated if SPIE in
SPCR is set and global interrupts are enabled. If SS is an input and is driven low when the SPI is
in Master mode, this will also set the SPIF Flag. SPIF is cleared by hardware when executing the
corresponding interrupt handling vector. Alternatively, the SPIF bit is cleared by first reading the
SPI Status Register with SPIF set, then accessing the SPI Data Register (SPDR).
Bit 6 – WCOL: Write Collision Flag
The WCOL bit is set if the SPI Data Register (SPDR) is written during a data transfer. The
WCOL bit (and the SPIF bit) are cleared by first reading the SPI Status Register with WCOL set,
and then accessing the SPI Data Register.
Bit 5:1 – Res: Reserved Bits
These bits are reserved bits and will always read as zero.
Bit 0 – SPI2X: Double SPI Speed Bit
When this bit is written logic one the SPI speed (SCK Frequency) will be doubled when the SPI
is in Master mode (see table 9.5). This means that the minimum SCK period will be two CPU
clock periods. When the SPI is configured as Slave, the SPI is only guaranteed to work at fosc/4
or lower. The SPI interface on the ATMEGA2560 is also used for program memory and
EEPROM downloading or uploading.
9.2.3 SPDR – SPI Data Register
Bit
Read / Write
Initial Value
7
MSB
R/W
X
6
5
4
3
2
1
R/W
X
R/W
X
R/W
X
R/W
X
R/W
X
R/W
X
0
LSB
R/W
X
The SPI Data Register is a read/write register used for data transfer between the Register File and
the SPI Shift Register. Writing to the register initiates data transmission. Reading the register
causes the Shift Register Receive buffer to be read.
9.3 Functions for SPI communication (Master)
9.3.1 SPI Master pin configuration (called inside the “port_init()” function)
void spi_pin_config (void)
{
DDRB = DDRB | 0x07;
PORTB = PORTB | 0x07;
}
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9.3.2 Function to configure SPI port for communication in master mode
//Function To Initialize SPI bus
// clock rate: 86400hz
void spi_init(void)
{
SPCR = 0x53; //setup SPI
SPSR = 0x00; //setup SPI
SPDR = 0x00;
}
9.3.4 Function to initialize SPI port
void init_devices(void)
{
cli(); //disable all interrupts
port_init();
spi_init();
sei(); //re-enable interrupts
}
9.3.5 Function to send a byte from the master and receive a byte from the slave device
//Function to send byte to the slave microcontroller and get ADC channel data from the slave microcontroller
unsigned char spi_master_tx_and_rx (unsigned char data)
{
unsigned char rx_data = 0;
PORTB = PORTB & 0xFE; // make SS pin low
SPDR = data;
while(!(SPSR & (1<<SPIF))); //wait for data transmission to complete
_delay_ms(1); //time for ADC conversion in the slave microcontroller
SPDR = 0x50; // send dummy byte to read back data from the slave microcontroller
while(!(SPSR & (1<<SPIF))); //wait for data reception to complete
rx_data = SPDR;
PORTB = PORTB | 0x01; // make SS high
return rx_data;
}
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9.4 Application examples
9.4.1 Application example: SPI master (ATMEGA2560)
Located in the folder “Experiments \ A_SPI_Master” folder in the documentation CD.
This program is for ATMEGA2560 (master) microcontroller. This program demonstrates SPI
communication between master (ATMEGA2560) and slave (ATMEGA8) microcontroller. LCD
displays analog values of the IR Proximity sensors 6, 7, 8 which are obtained from the
ATMEGA8 (slave) microcontroller.
Notes:
1. Setting for ATMEGA2560 (master) microcontroller
Make sure that in the configuration options following settings are done for proper
operation of the code
Microcontroller: ATMEGA2560
Frequency: 14745600
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
2. ATMEGA2560 (master) and ATMEGA8 (slave) microcontrollers use SPI bus for ISP as well
as for the communication between them. Before doing ISP we need to disconnect the SPI bus
between these two microcontrollers. Remove tree jumpers marked by J4 on the ATMEGA2560
microcontroller adaptor board before doing ISP.
3. Connect 3 jumpers marked by J4 to connect SPI bus between the microcontrollers.
4. Do not pass value more than 7 to the function "spi_master_tx_and_rx" else it will give back
random value
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9.4.2 Application example: SPI slave (ATMEGA8)
Located in the folder “Experiments \ B_SPI_Slave” folder in the documentation CD.
This program is for ATMEGA8 (slave) microcontroller. This program is the default firmware for
the ATMEGA8 (slave) microcontroller. This program demonstrates SPI communication between
master (ATMEGA2560) and slave (ATMEGA8) microcontroller. LCD displays analog values of
the IR Proximity sensors 6, 7, 8.
Note:
1. Make sure that in the configuration options following settings are done for proper operation of
the code
Microcontroller: atmega8
Frequency: 8000000
Optimization: -O0
(For more information read section: Selecting proper optimization options below figure
2.22 in the software manual)
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