Easy PIC Development Kit 877A - User Manual

Easy PIC Development Kit 877A - User Manual

Easy PIC Development Board

User Manual

1st Edition

April 2005

How to use this manual.

In an effort to enable PICSTERS with the appropriate skill set needed to make this course as rewarding as possible, this manual provides detailed information and walks you through the stages of developing your own codes. This manual is divided into four parts. There is a lot of material here, but you may not use all of it for your project.

PARTS

I.

The Easy Pic Development Board: Design and Assembly - This part introduces the features of the Easy Pic Development Board and gives some background information on its design.

II.

Getting Started: Programming the PIC - The second part provides you with a brief review of assembly language programming and the PIC instruction set. Here you will find a template that you can use as a starting point for writing your own assembly language program. This part concludes with instructions on assembling your assembly language program and downloading object code to the PIC microcontroller.

III.

BootLoader: This part describes how the actual user codes work with the bootloader. This will explain how to load the bootloader program and how to load the user code on the bootloader.

IV.

The Easy Pic Development Board: In Action - This part contains the information you need to make your Easy Pic Development Board actually do something. It begins by introducing the operation of the Easy Pic Development Board in two modes. One mode is bootloader mode and another one is Programmer mode. It then steps through the features of the PIC microcontroller, one-by-one, complete with instructions, diagrams, sample code and working examples. Equipped with the information provided here, you will be able to unleash the full capabilities of the Easy Pic

Development Board.

V.

Appendices - These are referenced by the three previous parts. Feel free to detach the appendices from the bulk of this manual; you will likely refer to them often.

This manual is intended to be a supplement to the PIC16F877A data sheet. The PIC16F877A data sheet includes absolutely everything you will need to know about the PIC16F87X microcontroller and this user manual refers to it often. Another helpful reference is the PICmicro Midrange Reference Manual. I would sincerely recommend taking the time to read this entire manual from beginning to end and to familiarize yourself with the data sheet; the things you will learn along the way will be helpful when it comes to designing your own project. Be aware, however, that completion of this manual will merely lay the groundwork for more interesting, albeit more useful, applications of the Easy Pic Development Board.

Keep in mind that the Easy Pic Development Board is just the central nervous system of your project. You are responsible for the design of the extraneous circuits that your project will utilize (sensors, motors, etc…). It would be prudent to make your initial circuit designs on this Easy Pic Development Board, then later transfer your design to a PCB CAD; to have it milled into a clean PCB. In general, rats nests of wires don’t hold up very well and, in accordance with Murphy’s Law, will inevitably let you down when you need them the most (during demonstrations of course!).

Contributors

This document was created by contributions from: Advanced Embedding and Packing solutions Pvt. Ltd.,

Future Tecknics Pvt. Ltd. and Winnii Solutions Pvt. Ltd. Chennai.

Table of Contents

Part I – The Easy Pic Development Board: Design and Assembly

1.0 Introduction to the Easy Pic Development Board

1.1 Easy Pic Development Board Specifications

1.2 Functional Description

1.2.1 DC Power Supplies

1.2.2 RS-232 Serial Interface

Part II – Getting Started: Programming the PIC

2.0 Programming the PIC Microcontroller

2.1 Assembly Language Programming

2.2 Memory Structure

2.3 Instruction Set

2.4 Subroutines

2.5 Interrupts

2.6 Putting It All Together

3.0 Assembling Your PIC Program

3.1 Developing your PIC program

3.2 Writing Your Program to the PIC

Part III – BootLoader

4.1 Introduction

4.2 How to use the bootloader

Part IV – Easy Pic Development Board: In action

5.0 Peripheral Features

5.1 I/O Ports –PortA,B,C,D & E

5.2 Led

5.3 7Segment

5.4 LCD Device

5.5 Key Switches

5.6 Analog to Digital Converter

5.7 Pulse Width Modulation

5.8 Relay

5.9 Buzzer

5.10 Master Synchronous Serial Port (MSSP)

5.10.1 Serial Peripheral Interface (SPI)

5.10.2 I2C

5.11 Universal Synchronous Asynchronous Receiver Transmitter (USART)

5.12 Timer Modules

Part V - How to use the Easy Pic Development Board

Part I

The Easy Pic Development Board:

Design and Assembly

1.0 Introduction to the Easy Pic Development Board

The Easy Pic Development Board is a compact, low power controller board that is based on the MicroChip

Technologies. This Easy Pic Development Board has a PIC16F877Aseries microcontroller. The PIC is the heart and soul of the Easy Pic Development Board, containing the central processing unit for the board.

The Easy Pic Development Board will be common to all projects with the addition of student designed and built circuits.

This Easy Pic Development Board comes loaded with the following features:

Communication Interfaces: RS-232 communication with a PC; SPI and I

2

C busses for communicating with other chips; and standard 5V CMOS digital I/O for anything else.

The PIC16F877A Easy Pic Development Board supports Parallel Slave Port Communication.

Extra Features: Three timer modules, a multi-channel analog-to-digital converter, two pulsewidth-modulated outputs, LCD Device, 7Segment Led, Key Switches, Relay, Buzzer and Led.

Additional Features of the PIC16F877 Easy Pic Development Board: Bootloader that allows you to develop and load your own code to the PIC without the need of Programmer

Two Methods to load the user program to the PIC:

BootLoader mode: BootLoader Mode is very useful for code development. Here Bootloader is used to load your code to the PIC.

Programmer mode: Programmer mode uses assembly code you have written and then “burned” to the PIC. This mode uses Programmer.

Complete with a relatively powerful processor and large I/O capability, the Easy Pic Development Board is an impressive control system. The range of projects is virtually limitless: you can control robots, perform wireless communication, carry out digital signal processing, or even connect your Easy Pic Development

Board to the Internet. The only limit is your imagination.

Peripheral Features

1) I/O Ports

2) LED

3) 7Segment LED

4) LCD Device

5) Key Switches

6) 10bit Analog to Digital Converter

8) Relay Operation

9) Buzzer

10) SPI Communication

11) I2C Communication

12) USART

13) Timer Modules

1.1 Easy Pic Development Board Specifications

These table lists the electrical characteristics of the Easy Pic Development Board, exceeding maximum values will very quickly damage your board.

Total Number of Pins on PIC (DIP package)

Range of Input Voltage to Barrel Connector

PIC Supply Voltage

Clock Speed

Digital I/O Pins

Analog to Digital Channels

Pulse Width Modulated Pins

10 Pin LCD Interface

PIC16F877A

40

6-18 Vdc

5 Vdc

4 MHz (Upgradeable to 20 MHz)*

33

8 (multiplexed)

2

Yes

Power Consumption with all IC’s

Max current drawn from +12Vdc connector

Max current drawn from +5Vdc connector

Max current drawn from -12Vdc connector

140 mA @ 16 Vdc

500 mA

500 mA

50 mA

Table 1.1 – Easy Pic Development Board Specifications

1.2 Functional Description

The Easy Pic Development Board is designed in a modular manner as shown in the block diagram below.

Refer to the Easy Pic Development Board schematic and board layout diagrams (found in appendix) as necessary to improve your understanding.

Figure 1.1 – Block Diagram of the Easy Pic Development Board Design

1.2.1 DC Power Supplies

Figure 1.2 – DC Power Supplies Schematic

DC power is supplied to the board through a 2.1mm coaxial barrel connector with center positive polarity.

Normally this power comes from a 18Vdc 500mA wall adaptor plugged into the barrel connector.

However, a 12Vdc 1A wall adaptor or suitably sized battery array can also be used. The Body or the barrel is negative supply.

Diodes D1 and D2 provide some reverse polarity protection and power supply transient isolation.

Capacitors C1 and C2 provide power supply bulk charge storage while C3-C6 provide additional power supply transient isolation for their respective supplies.

IC1 (7805) regulates the bulk supply to the +5Vdc needed for the PIC micro-controller and logic devices

(logic side of MAX232,LCD, 7Seg Display etc). IC2 (7812) and its components regulate the bulk supply for the Relay.

You will notice that the polarized capacitors have a non-polarized capacitor in parallel with them. This is not always necessary in designs but is here. The reasoning is that real capacitors are not ideal capacitors: larger capacitors tend to have greater amounts of intrinsic inductance associated with them due to their construction. Their greater inductance gives them poorer high frequency performance. Smaller capacitors tend to have better high frequency performance. Therefore, multiple real capacitors are used to approximate the required ideal capacitor performance.

1.2.2 RS-232 Serial Interface

The RS-232 circuitry consists of a DB9 female connector, the MAX232 and related circuitry. The DB9 connector is configured for an IBM PC-style 9-pin RS-232 connection. The MAX232 converts the RS-232

(sometimes called the HIN232) +/-12V signals to logic levels for the micro-controller. The resistors (330

Ω) limit line slew rates and provide some short circuit protection. The resistors R23, R24 (not shown here, see

Appendix A – Easy Pic Development Board Schematic Diagrams), R33 and R34 provide output contention protection (contention is created if the Digital I/O pin of PIC incorrectly configured as an output and is connected to the output of the MAX232). C24—C25 are used by the on-board charge-pump (note that the supply is +5V and yet the IC can deliver RS-232 level signals).

Figure 1.3 – RS-232 Serial Interface Schematic

Part II

Getting Started:

Programming the PIC

2.0 Programming the PIC Microcontroller

The main focus of this manual is assembly language programming of the PIC microcontroller. You will have access to a C compiler in your lab, however, the discussion on programming the PIC in C is limited and you will likely need to seek other resources.

2.1 Assembly Language Programming

Here we will review some of the basics of assembly language programming. First it is important to understand the memory structure of the PIC16F877A microcontroller. For detailed information on memory structure see the PIC16F877A data sheet.

2.2 Memory Structure

There are three memory blocks:

Program memory

Data memory

EEPROM data memory

1.Program Memory

The program memory is, as you may have guessed, the section where your program instructions are stored.

The size of the program memory for the PIC16F877A is 8Kx14 which means that it can hold 8x1024=8192

14-bit instructions.

The program memory is divided into 2K blocks called pages. So it has 4 pages. In order for commands on a certain program memory page to be executed the corresponding page must be selected. To switch between program memory pages use the pagesel directive.

A recommended way to use the pagesel directive is to first define the following values at the beginning of your assembly language program as follows (also see section 3.6): page0 EQU 0x0000 ; start address of page0 page1 EQU 0x0800 page2 EQU 0x1000

; start address of page1

; start address of page2 page3 EQU 0x1800 ; start address of page3

Then to select a page, say page 2 for example, use the following in the body of your main program: pagesel page2 ; selects program memory page 2

2.Data Memory

The data memory is divided up into 4 banks (bank 0-bank 3) that contain both Special Function Registers and General Function Registers. The special function registers are named and have a predefined function.

They are used for controlling the operation of the microcontroller. General function registers are used for data storage. The PIC16F877A has 368 8-bit general function registers.

To access a register in a certain data memory bank you must ensure that the appropriate bank is selected.

The status of the bank select bits, RP0 and RP1 (located in the STATUS register), determine which data memory bank is active. For example, to access the general-purpose register at address 0xA0 you must select bank 1 (i.e. RP1:RP0 =01).

The banksel directive can also be used to select the desired data memory bank, similar to the way in which the pagesel command is used to select the desired program memory page. First define the following values:

BANK0 EQU 0x0000 ; Data Memory start positions

BANK1 EQU 0x0080

BANK2 EQU 0x0100

BANK3 EQU 0x0180

Then to select the bank, say bank1 for example, use the following in the body of your main program: banksel BANK1 ; select data memory bank 1

3.EEPROM Memory

The EEPROM memory is nonvolatile meaning its contents are not erased when you turn off the power to the PIC. This is useful for storing information such as the state of your system before it is powered-down since this information can then be retrieved when the system is powered-up again. Data stored in the Data memory section (RAM) is erased when the power is removed from the PIC.

2.3 Instruction Set

The PIC16F877A uses a RISC-based architecture with only 35 instructions. See the PIC16F877A data sheet for instruction descriptions. Some of the more common instructions will be reviewed here.

An instruction is either byte-oriented or bit-oriented. The following bits of a register. bcf STATUS , RP0 ; Clear the RP0 bit in the STATUS register. bsf STATUS , RP1 bcf STATUS , RP0 bcf STATUS , RP1

; Set the RP1 bit in the STATUS register.

; Anything after a semicolon is a comment.

Remember that the RP0 and RP1 bits are used to select the data memory bank. The instructions above will select bank 1 (i.e. RB0:RB1=01).

The following is an example of a byte-oriented instruction. clrf STATUS ; Clear the entire STATUS register.

Many instructions use the ‘W’ register, which you can think of as a temporary storage place. To store a value in one of the general-purpose registers, say at address 0x20 (in bank 0), you could use the following commands:

; select bank 0 movlw movwf

0x35

0x20

; writes 0x35 to the W register

; moves the value from the W register to the

; general purpose register at address 0x20

To make your code more readable you can define labels to replace numerical values. These labels are defined at the beginning of your program using the EQU (equate) assembler directive. length EQU 0x35 ; Equate the label length with value 0x35. lreg EQU 0x20 ; Equate the label lreg with value 0x20.

With these defined the above instructions could now be replaced with: movlw length ; Load the W register with the value 0x35. movwf lreg ; Move the value from the W register to the

; General-purpose register at address 0x20.

An additional benefit to using labels is that if you decide to change any one of the values in your source code, you need to only change the value of the label rather than having to search through your entire source code for every occurrence of that value.

2.3.1 Mathematical Operations

Mathematical operations can be difficult since the instruction set includes commands only for addition and subtraction and there are no hardware floating-point operations. If you require this functionality in your code, there are some software emulation libraries that can be found on the microchip Webster

( www.microchip.com

), but they are not always easy to find. Try a search for ‘math emulation’. When programming in C, many of the advanced math functions are available to you. addwf lreg , W ; Add the contents of W and lreg and stores

Here the W register is the destination for the result of the addition, as specified by the second argument to the instruction. Alternatively, you can specify lreg to be the destination register by replacing W with F

(file). addwf lreg , F ; lreg is now the destination register

2.3.2 Flow Control

You can control the flow of your program using conditional or unconditional branches. Conditional branches (i.e. btfss, btfsc, incfsz, decfsz) test the value of the operand and branch accordingly. An example of an unconditional branch is the goto instruction.

A useful technique to use with flow control is ‘labeling’. You can label locations in your program and branch to that location using the label name. For example: bcf STATUS , RP0 ; Select bank 0.

LOOP decfsz lreg , F ; Decrement the value in the lreg goto goto

:

LOOP

ZERO

ZERO

{instructions}

:

; instruction if the result is 0.

; Branch to LOOP if result not 0.

; branch to ZERO if result is 0.

2.4 Subroutines

Using subroutines is a way to make your program modular. It also shortens the length of your main program making it easier to follow.

You can think of subroutines as mini programs that are called from the main program. Subroutines are usually defined after the main program. Consider the code below: main

{main program instructions}

: call incW

:

; call incW subroutine goto main ; return to beginning of main program

; subroutines are declared here incW incf W ; increment the value in the W register 3 times return ; return to main program

Here a subroutine called incf W is defined. The purpose of the subroutine is to increment the value in the

W register 3 times. In the main program you call the subroutine using the call instruction with the subroutine name as the operand. When the call command is executed the main program jumps to the incf

W subroutine, executes the commands defined there, then returns to the main program when the return instruction is executed.

Unlike many other microcontrollers, the PIC contains no user-accessible stack. Adding the fact that the programmer’s model contains only one working register, subroutines passing more than a single byte need to make use of the file register memory. Additionally, the stack in the PIC16F877a devices is only 8 locations deep. Recursive calling is thereby discouraged. Interrupts, described next, also require stack locations and reduce the possible call-depth.

2.5 Interrupts

Interrupts are an alternative to polling for events and can make processing time more efficient, since your program doesn’t need to wait for selected events to occur by polling. Every time a selected event triggers an interrupt, the PIC stops execution of the program and jumps to the interrupt service routine. Once finished, the PIC resumes normal execution of your program, where it left off.

Each of the built-in modules has the ability to cause an interrupt for one reason or another. The ADC, for example, can cause an interrupt when it has completed a conversion while the UART can produce an interrupt when its transmit buffer is empty or when its receive buffer is full.

When an interrupt occurs, the PIC jumps to the program memory location 0x0004, the interrupt vector. The program space available in this location is very limited so it’s recommended that you place your interrupt service routine (ISR) elsewhere in program memory and just put a GOTO command in the interrupt vector space.

For Ex:

0X0000

Goto Start

ORG

Goto Isev

Start Write your codes here

Isev Write your Interrupt subroutine here

End

Compared with other microcontrollers, the PIC16F877A family has a few notable differences with respect to interrupt processing.

1. Only one interrupt vector is used. Your ISR must determine (through status bits) which subsystem generated the interrupts.

2. Context of the CPU is not saved, except for the return Program Counter. Your ISR must be written to compensate for this.

3.Each interrupt uses one internal stack location until processing is complete. Only 8 stack locations are available and subroutine calls also use them. Due to this limitation, use of nested interrupts is discouraged.

However, nesting is disabled by default.

2.6 Putting It All Together

Now you are almost ready to write our own PIC assembly program. You can use any text editor to write your source code as long as you save it with a .asm extension. It is recommended that you use MPLAB, a free program provided by Microchip, to write and compile your source code. You can download a copy of

MPLAB from the Microchip website ( www.microchip.com

) .

Below is a very simple program that is used to show the necessary components for an assembly program.

Also, MPLAB contains source code templates (f873temp.asm and f877temp.asm), which can be found in

mplab/template/code/. You can use these as a starting point.

;

;

;

;

;

;************************************************************

;

; This is a program header. Here you give a brief

*

*

; description of what your program does and any other *

; important information about it. You should include *

;

; the name of the program, your name, the date you wrote the program and/or the last date it was

*

* modified. Include a course name if applicable. name: example.asm date: 9 July 2002 created by: Murali

(program name)

(date created)

(that’s me)

*

*

*

*

*

;

;

;

;

*

This program doesn’t do anything (since there are no * instructions in the main program). It is just used * to illustrate the necessary components of an assembly *

;

; language program for the PIC microcontroller.

;************************************************************ list p=16f877 ; this tells MPLAB which PIC

*

*

; use p=16f877 when necessary.

#include <p16f877.inc> ; this file defines the names and p16f877.inc necessary.

; The following commands set the PIC’s configuration bits. For now

; you don’t really need to understand how the configuration bits

; affect anything, but if you really want to see section 12.1 in the

; PIC16F87X data sheet.

; You can also set the configuration bits manually when you are

; downloading your program to the PIC (see section 4.1)

__CONFIG _CP_OFF & _WDT_OFF & _BODEN_OFF & _PWRTE_OFF & _XT_OSC &

_WRT_ENABLE_ON & _LVP_OFF & _CPD_OFF

; Label Definitions

TEMP1

TEMP2

EQU 0x20

EQU 0x21

BANK0

BANK1

BANK2

BANK3 page0 EQU page1 EQU page2 EQU

EQU 0x0000

EQU 0x0080

EQU 0x0100

EQU 0x0180

0x0000

0x0800

0x1000

; Data Memory start positions

; for use with banksel directive

; see section 3.2

; program memory start positions

; for use with pagesel directive

; see section 3.2 page3 EQU 0x1800

; This is where your program code begins

ORG movlw 0x00

0x00 movwf PCLATH goto Main

; when the PIC is powered up or after a reset

; the instruction at address 0x00 is the first

; to be executed. The ORG instruction tells

; the device programming the PIC to start

; writing the following instructions at the

; address indicated (in this case at address

; 0x00).

; selects page0 of the program memory

; jumps to beginning of your program

; Only include this next section if you are using interrupts.

ORG 0x04 goto Service

; when an interrupt occurs the program jumps

; to the instruction at address 0x04

; jumps to the subroutine ‘service’, which will

; this is the start of your main program

Main

{the instructions for your main program go here.}

; this is the interrupt service routine

Service

{the instructions for your interrupt service routine go here.}

END ; this is the end of the program.

The source code for some example programs is available on the CD Disk. It may help to take a quick look at the code to become more familiar with the contents of an assembly language program.

3.0

Assembling Your PIC Program

It has the following two parts.

3.1 Developing Your PIC Program

To actually make your Easy Pic Development Board “do” anything, it needs to be running a program. In this section you will use MPLAB to develop your own assembly code. In the next section you will burn the program’s object code to your Easy Pic Development Board.

To develop and assemble the program, follow these steps:

MPLAB

2. Create New Project ( Project New)

3. Create New File (File New)

4. Write Your assembly code

5. Add your source code to the Project. (Project Add files to project)

6. Compile your source code. (Project Build All)

And that’s it. A new window will open that shows the results of the process. If your source code is error free the message ‘Build Completed Successfully.’ will appear in this window. Assembling generates a

*.hex file and places it in the same directory as your source code file. This is the file that you will download to the PIC microcontroller. You can also copy the *.hex file from the Disk.

If there are errors in your code then this window will contain the appropriate error messages.

3.2 Writing Your Program to the PIC

The PIC has a flash type program memory, which can be written, erased and rewritten. This is very useful for debugging (you can test out the capabilities and connections of your circuitry before letting your project run amuck). Typically the flash memory can go through several thousand of these cycles so you don’t need to worry about it breaking down on you.

Here we are providing two methods to burn a program to the PIC. These are Bootloader mode, programmer mode. Bootloader mode is explained in the next Section. In this section you will see the Programmer mode.

You should buy any programmer to burn your program to the PIC. Before using the Programmer, you should read the manual given with it. The manual describes how to put the PIC on the Socket. The position

where you place the PIC is very important. If you do anything wrong that will permanently damage your

Programmer and destroys your PIC.

They will provide the user-friendly software to do the following

Select the PIC to burn

Select the hex file

Configure the PIC

Erase the codes in the PIC

Read the PIC

Burn the program to the PIC

Using the software burn the program to the PIC. You will receive a message notifying you if the program was transferred to the PIC successfully. Take the PIC out of the Programmer, plug it backs into your Easy

Pic Development Board, and you’re ready for business.

Part III

PIC 16F8xx Boot Loader

4.0 Introduction

A bootloader is used to quickly download a new program into your PIC micro, in a few seconds. Once you have it set up, you can quickly update the .hex file in your PIC micro with a single keystroke. Bootloading is easily performed in-circuit, with the PIC micro still plugged into your PCB.

BootLoader reserves top 255bytes in the Program memory. If you use this bootloader, you can’t use the upper 255 bytes for your normal program. As well as you should also include the following four additional lines in your assembly program.

Org 0x0000 (These four lines should be included)

Movlw

Movwf

Goto

Nop

0x00

PCLATH

Main

Org

Goto

Main

0x0004

Isev

:

Isev

:

:

End

:

For CCS C language you don’t need to include any additional lines.

4.1 How to use the BootLoader

• The PIC 16F877A that we have given to you has already programmed with the bootloader code. If any case it lost, load bootloader.hex file to the PIC. For this purpose you should use any programmer.

• Put that PIC on the Zip Socket on the given board.

• Plug in the RS232 serial adapter to your Board.

• Give the power supply to the board.

• Use MPLAB for your code creation and corrections.

• Compile with MPLAB to produce *.Hex file

• If finished, open PIC Bootloader+ Software. (

BootL Sw\PICbootPlus.exe

) That window is look like the below figure.

• Set baud rate is 9600.

• Select the Com Port which will be used (you will need one free com port on your system).

• Click the search button to select your .hex file.

• Click Write button on the window software, then press the reset key on the board to burn your hex file to the PIC

• If everything is ok, you will see the OK message in the info box.

• The bootloader remains active for 0.2 seconds after reset, to give you the option of uploading new code, and after 0.2 seconds (or uploading complete) you can use the serial port as normal and also it executes the user code.

• If not, it will display the relevant error message

Figure: BootLoader

Part IV

The Easy Pic Development Board in Action

5.0 Peripheral Features

This section will explain the features of the Easy Pic Development Board. It has following features

Ports

2) LED

3) 7Segment LED

4) LCD

Switches

6) 10bit Analog to Digital Converter

Width

8) Relay

9) Buzzer

10) SPI Communication

11) I2C Communication

12) USART

13) Timer Modules

5.1 I/O Ports

The PIC16F877 has 33 I/O pins, divided into 5 ports (Port A-Port E), which can be configured in various ways to communicate with many different peripheral devices. Port A has 6 pins, Port B-Port D each have 8 pins and Port E has 3 pins.

Many of these pins are multiplexed with more than one function. You can control the function of each pin

(or group of pins) by writing the proper value to the appropriate Special Function Register.

The simplest function for these pins is general purpose digital I/O. You can configure any pin as a digital output and set its value high (+5V) or low (0V), or configure it as a digital input and read its present value.

Each port has an associated PORTx register (bi-directional port) and a TRISx register (data direction register). Setting a bit in the TRISx register makes the corresponding pin an input, clearing the bit makes it an output. For example, setting bit 4 in the TRISB register makes pin RB4 an input. Setting a bit in the

PORTx register sets the corresponding pin high (as long as it is configured as an output). Clearing the bit set the pin low. For example, setting bit 3 in the PORTC register sets the output pin RC3 high. Data is input by reading from the PORTx register.

The following code is an example of how to implement this in your program. bsf bcf movlw movwf bcf

STATUS , RP0

STATUS , RP1

B’11110000’

TRISB

STATUS , RP0

; select bank1

; configure RB7:RB4 as inputs

; configure RB3:RB0 as outputs

; select bank0 movf PORTB , W ; reads inputs and stores in W register movlw B’1010’ ; sets outputs RB3 and RB1 high, movwf PORTB ; RB2 and RB0 low

Each port, and the alternate function(s) of its pins, is discussed in its own section below. Refer to section

3.0 of the PIC16F87X data sheet for additional information on I/O ports.

5.1.1 Port A

In this section port A is discussed. It is multiplexed with analog inputs (with the exception of pin RA4, which is multiplexed with the Timer0 module). Instead of Port A, Port E is also multiplexed with analog inputs but in this board these pins are used to control Relays and Buzzer. So you have only 5 analog channel instead of 8. In these five channels, 3 channels are connected internally and analog voltage is controlled through POT. The remaining two channels is used for the external analog input.

The function of each pin in this port is selected using the A/D port configuration control bits (the lower four bits of the ADCON1 register). Refer to Section 11.0 (Register 11-2) in the PIC16F877A data sheet for a table of the A/D port configuration control bits.

For example, to configure all the pins in ports A and E for general purpose digital I/O you must write

B’011x’ (B’0110’ or B’0111’) to the lower four bits of the ADCON1 register.

The analog inputs are used with the Analog-to-Digital Converter (A/D) module. See section 6.7 for instructions on using the A/D module. The ADON bit (ADCON0<0>) controls whether or not the A/D module is operating. If you are not using the A/D module then it is recommended that you turn it off by clearing the ADON bit.

Data is read from/written to ports A and E using the PORTA and PORTE port registers, respectively. The data direction registers are TRISA and TRISE.

Table 6.1: Summary of Registers Associated with PORTA.

The following code shows how ports A can be initialized for digital I/O: bcf bcf

STATUS , RP0

STATUS , RP1

; select bank0 clrf bsf

PORTA ; clear ports A to initialize bcf

STATUS , RP0

STATUS , RP1 movlw b’0110’ movwf ADCON1

; select bank1

; configure ports A and E for

; digital I/O movlw b’111000’ movwf TRISA

; set RA5:RA3 and RE0 as inputs

; RA2:RA0 and RE2:RE1 as outputs

5.1.2 Port B

Port B is a general purpose Digital I/O Port. Data is read from/written to port B using the PORTB port register. The data direction register.This Port is multiplexed with following function

• Glow the led in output mode

• Get the input through Key Switches

• Control the multiplexed 7Segment LED

This Port has following features

Support External Interrupt in RB0

Support the interrupt-on-change in RB4-RB7

Table 6.2: Summary of Registers Associated with PORTB.

Name Address Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

PORTB

TRISB

0x06

0x86

RB7 RB6 RB5 RB4 RB3

PORTB data direction bits.

RB2 RB1 RB0

OPTION_REG

5.1.3 Port C

0x81 RBPU INTEDG T0CS T0SE PSA PS2 PS1 PS0

Port C is shared by many of the peripheral functions, such as the timer modules, the pulse-width-modulator, the analog-to-digital converter and the serial communication modules

Data is read from/written to port C using the PORTC port register. The data direction register is TRISC.

Table 6.3 Summary of Function Associated with PORTC

No Port Pins No

1 RC1,RC2

Functions

Pulse Width Modulation

2

3

4

RC0,RC3-RC5

RC3,RC4

RC6,RC7

SPI

I2C

USART

Table 6.3: Summary of Registers Associated with PORTC.

Name Address Bit 7 Bit 6 Bit 5 Bit 4 Bit 3

PORTC 0x07 RC7 RC6 RC5 RC4 RC3 RC2 RC1

TRISC 0x87

PORTC data direction bits.

5.1.4 Port D

Port D is multiplexed with the Parallel Slave Port (PSP) module. To disable the PSP module the

PSPMODE bit (TRISE<4>) must be cleared.

Name Address Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1

PORTD

TRISD

0x08

0x88

RD7 RD6 RD5 RD4 RD3

PORTD data direction bits.

TRISE 0x85 IBF OBF IBOV PSPMODE

Table 6.4: Summary of Registers Associated with PORTD.

Bit 2

RD2

Bit 1

RD1

PORTE data direction bits.

Bit 0

RC0

Bit 0

RD0

In this board PORTD is multiplexed with LCD Device and 7Segment LED.LCD Device uses RD0-RD6 pins (RD0-RD3 Control Lines (Rs, Rw and Es), RD4-RD6 Data Lines). Here this board has multiplexed six 7segment LED. This uses Port D for data line and Port B for segment selection.

Data is read from/written to Port D using the PORTD port register. The data direction register is TRISD.

5.1.5 Port E

Port E is multiplexed with analog input. But here these pins are dedicated to some other application like

Relay operation (RE0, RE1) and Buzzer (RE2).

Data is read from/written to Port D using the PORTD port register. The data direction register is TRISD

Table 6.4: Summary of Registers Associated with PORTE.

5.2 LED

In this board Led is connected in Port B. LED is used to indicate the pin status. There is a Jumper to enable or diable the Led’s.

Program which uses the LED function:

Assembly File Hex File

Flash.asm (

Example\Flash.asm

)

Flash.hex )

Shifting.asm (

Example\Shifting.asm

)

Shifting.hex

)

5.3 7Segment LED

Here we have six 7Segment Led. These are multiplexed with one another. This function uses Port D and

Port B. Port D is used to send the data to the Segment and Port B is used to select the particular Segment to

Glow.

You have already known the 7Segments are multiplexed with the LCD. Before proceeding it you should select 7segment display by changing the jumper to 7Seg position (See the Easy Pic Development Board).

Port B is multiplexed with the keyswitches, so changing the jumper to LED position

Program which uses the 7Segment LED function:

Assembly File Hex File

7segment.asm ( Example\7Segment.asm

) ( Example\count.HEX

)

Multiplex.( Example\Multiplexing.asm)

Arith.asm ( Example\arith.asm)

Adc.asm ( Example\Adc_volt.asm

)

Multiplex (

Arith.hex (

Adc.hex (

Example\Multiplexing.HEX)

Example\arith.HEX)

Example\Adc_volt.HEX

)

Load the hex file to the PIC and see the output

.

If anything goes wrong check the power socket,& Jumper position

.

5.4 LCD Device

Now you knew this device is multiplexed with 7Segment.And you also knew it uses Port D for both control and data lines. Before using this device you should change the jumper position to LCD Device. (See the

Board)

Program which uses the LCD function:

Assembly File

Lcddisplay.asm (

Example\LcdDisplay.asm)

Acd_lcd.c (

Example\Adc_Lcd.c

)

Scanning.c (

Example\AdcScan.c)

Eeprom.asm (

Example\EepromLcd.asm)

Hex File

Lcddisplay.hex (

Acd_lcd.hex (

Scanning.hex (

Eeprom.hex (

Example\LcdDisplay.HEX)

Example\AdcScan.HEX

)

Example\EepromLcd.HEX)

5.5 Key Switches

Key Switches are multiplexed with 7segment devices. Key switches are connected from RB0-RB5. You can use this key switches after changing the jumper to key position (See the Board).

Program which uses the Key Switches:

Assembly File Hex File

RB0interrupt (

Example\RB0Interrupt.asm

)

(

Example\RB0interrupt.HEX

)

stopwatch (

Example\StopWatch.asm

)

Stopwatch

)

Scanning.c (

Example\AdcScan.c

)

(

Example\AdcScan.HEX

)

5.6 Analog to Digital Converter

The PIC 16F877A has 8 channels, 10bit Analog to Digital Converter. These eight channels are multiplexed together; the ADC can only sample one input at a time. Here Port A has five channels and Port E has remaining 3 channels. But in this board Port E pins are used for some other purposes, so you can use only

PortA analog pins.

In this board 3 channels are directly connected with internal circuit Power through a Variable POT. The

POT is used to change the analog input voltage given to the pin. The other two channels are used to scan the external analog inputs. You should take care about the external input; its range should be in between 0-

5V DC.

The entire ADC pins have a limited amount of diode protection to prevent input voltages outside of the

Vdd to Vss range. A better way to make sure your PIC doesn't get fried by stray analog voltages though, is to set up a small circuit before the signal reaches the ADC pin similar to the one to the right. This circuit will not let any voltage hit the ADC pin unless it is between 0 and 5V and doesn't depend on the PIC's limited protection.

The PIC16F877A data sheet also recommends that the maximum input impedance of an analog source be less than 10kΩ and that any current on any pin should not exceed ±20mA

.

ADC converts the given analog inputs to the 10bit digital output. It is stored in the register ADRESH,

ADRESL. This conversion uses TRISA, PORTA, ADCON0 and ADCON1 register. Refer 16F877A datasheet for further need

Program which uses the ADC:

Assembly File

Adc.asm ( Example\Adc.asm

)

Acd_lcd.c (

Example\Adc_Lcd.c

)

Scanning.c (

Example\AdcScan.c)

Hex File

Adc.hex (

Example\adc.HEX

)

Acd_lcd.hex (

Scanning.hex (

Example\AdcScan.HEX

Relay.asm ( Example\Relay.asm

) Relay.hex )

Adc_volt (

Example\Adc_volt.asm

) Adc_volt (

Example\Adc_volt.HEX

)

)

5.7 Pulse Width Modulation

You can think of the Pulse Width Modulator as a square wave generator where the period and duty cycle are variable. There are 2 PWM outputs (CCP1 and CCP2) and they may have different duty cycles but they share a common period.

The PWM period is calculated using the following formula:

You have control over the value in the PR2 register (Timer2 module’s register) and the TMR2 prescale value. PR2 holds an 8-bit number and TMR2 prescale value can be either1, 4 or 16. TMR2 prescale value is set using the T2CKSP1:T2CKSP0 bits (T2CON<1:0>). See section 7.0 (Register 7-1) in the PIC16F87X data sheet. Tosc is the oscillator period (0.25

μs).

For example, if PR2 contains B’01100111’ = 103 and T2CKSP1:T2CKSP0 = B’01’ (prescale = 4) then the

PWM period is (103+1)*4*0.25*4 = 416

μs.

The duty cycles are specified with a 10-bit number. Each PWM pin has an associated CCPRxL register and

CCPxCON register. The CCPR1L register holds the upper 8 bits of the duty cycle value for CCP1 and

CCP1CON<5:4> holds the lower 2 bits. For CCP2 the CCPR2L and CCP2CON registers are used. The following equation defines the PWM duty cycle:

For example, if CCPR1L contains B’00110011’ and CCP1CON<5:4> contains B’10’ the duty cycle for

CCP1 is 206*0.25*4 = 206

μs.

Program which use the PWM:

Assembly File

Pwm.asm ( Example\Pwm.asm

)

Hex File

Pwm.hex (

Example\Pwm.HEX

)

5.8 Relay

The PIC has a 25mA current drive capability and this current is quite good for most low power circuits.

Sometimes a component like a motor or light bulb may need to be controlled by a PIC output pin and more than likely, these types of components will draw more than 25mA which can be supplied by the PIC pin.

Figure: Relay

One way around this problem is to use a relay to switch the high currents needed. In some cases, a relay can be connected directly to the PIC, but usually a transistor is used. A transistor requires only a small base current to let a much larger current flow through it’s collector. Also, the component that the transistor is switching can have an operating voltage higher than the 5 volts supplying the PIC. This makes it an ideal component to control relays from the IO pins of the PIC.

The relay supplied with this board has an operating voltage of 12 volts.

Program which use the Relay:

Assembly File

Relay.asm (

Example\Relay.asm

)

Hex File

Relay.hex ( Example\Relay.HEX)

5.9 Buzzer

Buzzer is connected in the pin RE2. Normally Buzzer is used to indicate some status to the user.This pin can be activated in your programs to audiable indications, like pressing of a key, confirmation, error etc.

Programs which use the Buzzer:

Assembly File

Buzzer (

Example\Buzzer.asm

)

Hex File

Buzzer ( Example\Buzzer.HEX

)

5.10 Master Synchronous Serial Port (MSSP)

The Master Synchronous Serial Port (MSSP) module is used for serial communication with peripheral devices. The MSSP module can operate in one of two modes:

Peripheral Interface (SPI)

2. Inter-Integrated Circuit (I

2

C)

These modes are multiplexed with each other. So you can use only one mode at a time. Before using

MSSP, you should remove the I2C or SPI ADC as appropriate. (see the board).

5.10.1 SPI

The SPI mode allows 8 bits of data to be synchronously transmitted and received simultaneously. All four modes of SPI are supported. To accomplish communication, typically three pins are used:

• Serial Data Out (SDO) - RC5/SDO

• Serial Data In (SDI) - RC4/SDI/SDA

• Serial Clock (SCK) - RC3/SCK/SCL/LVDIN

Additionally a fourth pin may be used when in a Slave mode of operation:

• Slave Select (SS) - RA5/SS/AN4

SPI mode uses following register:

• MSSP Control Register (SSPCON)

• MSSP Status Register (SSPSTAT)

• Serial Receive/Transmit Buffer (SSPBUF)

• MSSP Shift Register (SSPSR) - Not directly

SSPCON and SSPSTAT are the control and status registers in SPI mode operation. The SSPCON register is readable and writable. The lower 6 bits of the SSPSTAT are read only. The upper two bits of the

SSPSTAT are read/write. SSPSR is the shift register used for shifting data in or out. SSPBUF is the buffer register to which data bytes are written to or read from.

In receive operations, SSPSR and SSPBUF together create a double-buffered receiver. When SSPSR receives a complete byte, it is transferred to SSPBUF and the SSPIF interrupt is set. During transmission, the SSPBUF is not double buffered. A write to SSPBUF will write to both SSPBUF and SSPSR.

This board has ADC MCP3202 to explain SPI operation. You can connect any other SPI device with the

SPI pins. Before that you should remove the ADC MCP3202 from the IC socket.

(See the Board).

Let us see how the SPI device connected with SPI pins:

External ADC (MCP3202) is a 12-bit analog-to-digital converter. There are two input channels available on the MCP3202.Both the inputs are multiplexed together, the ADC can read only one input at a time.

Using the SPI, MCP3202 is connected to PIC16F877A. Pin Diagram of MCP3202 and Function of each pin is as follows:

Figure 6.2: MCP3202 Pin Diagram

Figure 6.3: MCP3202 Pin Function Table

Consider the following schematic:

Figure 6.4: Schematic – External ADC Using SPI

The above schematic explains how to connect the external peripheral to the PIC. You should read the datasheet for peripheral before using it.

Programs which use the SPI Function:

Assembly File

Adc

Example\ExternalAdc.asm

Hex File

Adc ( Example\ExternalAdc.HEX

)

5.10.2 I2C

The MSSP module in I2C mode fully implements all master and slave functions (including general call support) and provides interrupts on START and STOP bits in hardware to determine a free bus (multimaster function). The MSSP module implements the standard mode specifications, as well as 7-bit and

10-bit addressing.

Two pins are used for data transfer:

• Serial clock (SCL) - RC3/SCK/SCL

• Serial data (SDA) - RC4/SDI/SDA

The user must configure these pins as inputs or outputs through the TRISC<4:3> bits

.

The MSSP module has six registers for I2C operation. These are:

• MSSP Control Register (SSPCON)

• MSSP Control Register 2 (SSPCON2)

• MSSP Status Register (SSPSTAT)

• Serial Receive/Transmit Buffer (SSPBUF)

• MSSP Shift Register (SSPSR) - Not directly accessible

• MSSP Address Register (SSPADD

Please refer the PIC datasheet for more information. It uses only two pins. Please remove the SPI device

(ADC MCP3202 ) from the board. This board has an EEPROM (24LS256) I2C device. Also you can connect any number of peripheral that support the I2C communication. This EEPROM (24LS256) I2C device is configured as device 1.

Programs which use the I2C Function:

Assembly File

I2C (

Example\i2c_24lc256.HEX

)

Hex File

I2C ( Example\i2c_24lc256.HEX

Load the above hex file to the PIC and check the result.

)

5.11 Universal Synchronous Asynchronous Receiver Transmitter (USART)

The Universal Synchronous Asynchronous Receiver Transmitter (USART) module is one of the two serial

I/O modules. (USART is also known as a Serial Communications Interface or SCI.) The USART can be configured as a full duplex asynchronous system that can communicate with peripheral devices, such as

CRT terminals and personal computers, or it can be configured as a half duplex synchronous system that can communicate with peripheral devices, such as A/D or D/A integrated circuits, serial EEPROMs etc

.

The USART can be configured in the following modes:

• Asynchronous (full duplex)

• Synchronous - Master (half duplex)

• Synchronous - Slave (half duplex)

Bit SPEN (RCSTA<7>) and bits TRISC<7:6> have to be set in order to configure pins RC6/TX/CK and

RC7/RX/DT as the Universal Synchronous Asynchronous Receiver Transmitter. The USART module also has a multi-processor communication capability using 9-bit address detection

.

Program which use the USART Function:

Assembly File

Usart.asm ( Example\Usart.asm

)

Hex File

Usart.hex ( Example\Usart.HEX

)

In this example the USART module will be used to communicate with a personal computer.

HyperTerminal (or other terminal program) on your PC is used to communicate with the Easy Pic

Development Board.

Easy Pic Development Board is connected using a computer serial cable. The male end of the cable connects to the DB-9 connector on your Easy Pic Development Board and the female end connects to one of the serial connectors (COM1 or COM2) on the back of your PC.

To properly communicate, both the HyperTerminal and the USART must be configured with the same settings. The below example program uses 9600 baud rate.

The mode of communication is Asynchronous since there is no clock signal. Instead start and stop bits are used. When asynchronous mode is selected the USART automatically attaches start and stop bits to the data.

We will only be sending byte size data chunks so 8-bit transmit and receive is selected. Hardware flow control will be used.

Now open and configure HyperTerminal with the following settings (refer to section 5.0 if necessary).

1. 9600 Bits Per Second.

2. 8 Data Bits.

3. No

4. 1 Stop Bits.

5. Hardware Flow Control.

Load the above program to the PIC and watch the output.

5.12 Timer Modules

Built into the PIC are three timer modules. Timer 0 is a general-purpose 8-bit timer/counter. Timer 1 is a

16-bit timer/counter that can be used with the capture/compare/PWM module. Finally, timer 2 is an 8-bit timer that is used to control the PWM module. Refer to sections 5-7 in the PIC16F87X data sheet for detailed instructions on using the respective timer modules.

Program which use the Timer:

Assembly File Hex File

Buzzer ( Example\Buzzer.asm

) Buzzer

Pwm ( Example\Pwm.asm

) Pwm )

Stopwatch ( Example\StopWatch.asm

) Stopwatch )

6.0 How to use the Board

Here we have given PIC 16F877A datasheet and Easy Pic Development Board Manual, Read the documents carefully. As well as we have provided some example files to you. Load the .hex file to the PIC using the Bootloader software (Refer Part III).

1) Check the jumper position (see Board feature- for LCD, LED, 7Seg & Key Switch).

2) Connect the RS232 cable connector to the Board Port and free com port of computer.

3) Connect the power / wall adapter.(18VDC, Barrel Ground, 500ma)

4) Upload the * .hex file to the PIC through Bootloader software.

5) Check for user file execution by the PIC.

6) To view the source code, open *.asm file in Mplab.

7) Make correction to *.asm file if necessary.

8) Compile source code with Mplab.

9) Repeat steps 4 to 8 as needed.

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