CHARACTER LCD INTERFACE EEM 336

CHARACTER LCD INTERFACE EEM 336

Anadolu University

Department of Electrical & Electronics

Engineering

EEM 336

Microprocessors 1

CHARACTER LCD INTERFACE

Liquid Crystal Display Module 24-202 is an optional accessory for the APPLICATIONS

BOARD. The module is ready to connect to P4 of the

APPS-BD. the 2 line by 20 digits LCD Module is

The LCD supports an 8-bit data interface and 4-bit data interface to implement data transfers.

In the lab sessions 8-bit data interface will be implemented.

All components in th LCD interface are fitted and a standard LCD module & cable supplied.

The LCD module is attached to the applications board via P4. When an LCD module is connected, preset pot VR2 should be adjusted to obtain the required contrast. Control of the LCD display is achieved by port 2 bits D0 – D7 and port 1 bits D0 – D2, this is summarized in table

2.4 of the manual

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. supplied mounted in an acrylic frame for ease of handling. This option is invaluable for demonstrating the display of messages, warnings or instructions, as used on small instruments or on large public information boards such as those found at stations, airports, etc. The techniques for rolling, flashing and alternating messages can be shown.

Port – Pin name Pin Function P4 – pin no

5 V

Pot VR2

Vdd

Vee (contrast)

2

3

Port 1 D0 (PORTB for HC11) RS (Instruction / Data) 4

Port 1 D1 R/W (Read / Write) 5

Port 1 D2 E (Enable)

Port 2 D0 (PORTC for HC11) DB0 (Data Bus)

6

7

Port 2 D1

Port 2 D2

Port 2 D3

Port 2 D4

Port 2 D5

Port 2 D6

Port 2 D7

DB1

DB2

DB3

DB4

DB5

DB6

DB7

12

13

14

8

9

10

11

1

FEEDBACK Microprocessor Applications Board Reference Manual 24-200

1

This document is a tutorial on generic character LCD programming techniques. The web version tutorial is edited

2

as a printable document to help students who attend embedded systems classes and is aimed to be a comprehensive resource on controlling character LCD displays.

Eventhough ASM and C codes given in this document are based upon ATMEL’s 8051 microcontroller family, once you understand the general principles; you can easily adapt them to any microprocessor family including Motorola’s 68HC1X and 68K families. Pin conversions are given on the previous page. You can use those pins to configure your LCD display attached to the applications board. A demonstration code segment is given below.

For HC11, you can easily define functions to set and clear LCD pins as following;

#include <hc11.h> // HC11 Ports are defined in this header

#define LCD_data PORTC // P2

#define LCD_rs 0x01 // P1_0 void set_LCD_rs( void ){

PORTB

} void clear_LCD_rs( void ){

PORTB

}

~LCD_rs;

You should also define similar functions for setting and clearing other LCD pins (rw, en). After defining set and clear functions, you can replace the rows “

LCD_rs = 1;

” of the c codes given in tutorial with “ set_LCD_rs();

” and etc… When your modifications are finished, you can run following sample code and check your LCD display;

// A sample code for controlling LCD display in HC11

// LCD functions should be defined as given in tutorial.

int main( void )

{ char *mytext = "LCD_test OK!" ;

DDRC 0xFF;

LCD_init(); // LCD display should be initialized first of all.

LCD_sendstring(mytext); return 0;

}

Important Note: In LCD_busy() function, you should change direction of PORTC_Pin7 as input (first row). At the end of function, its direction should be restored as output (append it to the code).

2

Edited by Research Asistant Sukru Gorgulu, May, 2010, Anadolu University, Eskisehir, TR

2

A TUTORIAL ON GENERIC LCD PROGRAMMING

The most commonly used Character based LCDs are based on Hitachi's HD44780 controller or other which are compatible with HD44580. In this tutorial

3

, we will discuss about character based LCDs, their interfacing with various microcontrollers, various interfaces (8-bit/4bit), programming, special stuff and tricks you can do with these simple looking LCDs which can give a new look to your application.

 

INTRODUCTION TO LCD .......................................................................................................... 4

 

Pin Description ..................................................................................................................... 4

 

BASICS OF LCD ........................................................................................................................... 6

 

DDRAM - Display Data RAM ............................................................................................. 6

 

CGROM - Character Generator ROM ................................................................................. 6

 

CGRAM - Character Generator RAM ................................................................................. 9

 

BF - Busy Flag ...................................................................................................................... 9

 

Instruction Register (IR) and Data Register (DR) ................................................................ 9

 

LCD COMMANDS ...................................................................................................................... 10

 

Commands and Instruction set ........................................................................................... 10

 

LCD INITIALIZATION ............................................................................................................. 13

 

Initialization by internal Reset Circuit ............................................................................... 13

 

Initialization by instructions ............................................................................................... 14

 

LCD Entry mode ................................................................................................................ 16

 

Programming example for LCD Initialization ................................................................... 16

 

CHECKING BUSY FLAG .......................................................................................................... 18

 

Reading the busy Flag ........................................................................................................ 18

 

SENDING COMMAND & DATA TO LCD .............................................................................. 20

 

Sending Commands to LCD ............................................................................................... 20

 

Setting cursor position on LCD .......................................................................................... 21

 

Sending Data to LCD ......................................................................................................... 21

 

CREATING CUSTOM CHARACTERS ................................................................................... 24

 

CGRAM and Character Building ....................................................................................... 24

 

INTRODUCTION TO USING LCD IN 4-BIT MODE ............................................................ 28

 

LCD connections in 4-bit Mode ......................................................................................... 28

 

Sending data/command in 4-bit Mode ............................................................................... 29

 

4-bit Initialization ............................................................................................................... 29

 

Sending Dommand/Data to LCD in 4-bit mode ................................................................. 31

 

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Tutorial Web Source: http://www.8051projects.net/lcd-interfacing/introduction.php

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INTRODUCTION TO LCD

Pin Description

The most commonly used LCDs found in the market today are 1 Line, 2 Line or 4 Line

LCDs which have only 1 controller and support at most of 80 charachers, whereas LCDs supporting more than 80 characters make use of 2 HD44780 controllers.

Most LCDs with 1 controller has 14 Pins and LCDs with 2 controller has 16 Pins (two pins are extra in both for back-light LED connections). Pin description is shown in the table below.

Figure 1: Character LCD type HD44780 Pin diagram

Usually these days you will find single controller LCD modules are used more in the market. So in the tutorial we will discuss more about the single controller LCD, the operation and everything else is same for the double controller too. Lets take a look at the basic information which is there in every LCD.

4

Pin No. Name Description

Pin no. 1

Pin no. 2

Pin no. 3

Pin no. 4

Pin no. 5

VSS

VCC

VEE

RS

R/W

Pin no. 6

Pin no. 7

Pin no. 8

Pin no. 9

Pin no. 10 D3

Pin no. 11

D4

Pin no. 12

D5

Pin no. 13 D6

Pin no. 14 D7

EN

D0

D1

D2

Power supply (GND)

Power supply (+5V)

Contrast adjust

0 = Instruction input

1 = Data input

0 = Write to LCD module

1 = Read from LCD module

Enable signal

Data bus line 0 (LSB)

Data bus line 1

Data bus line 2

Data bus line 3

Data bus line 4

Data bus line 5

Data bus line 6

Data bus line 7 (MSB)

Table 1: Character LCD pins with 1 Controller

Pin No. Name Description

Pin no. 1

Pin no. 2

Pin no. 6

Pin no. 7

Pin no. 8

Pin no. 9

D7

D6

Pin no. 3 D5

Pin no. 4

D4

Pin no. 5 D3

D2

D1

D0

EN1

Pin no. 10 R/W

Pin no. 11 RS

Pin no. 12 VEE

Pin no. 13 VSS

Pin no. 14 VCC

Pin no. 15 EN2

Pin no. 16 NC

Data bus line 7 (MSB)

Data bus line 6

Data bus line 5

Data bus line 4

Data bus line 3

Data bus line 2

Data bus line 1

Data bus line 0 (LSB)

Enable signal for row 0 and 1 (1 st controller)

0 = Write to LCD module

1 = Read from LCD module

0 = Instruction input

1 = Data input

Contrast adjust

Power supply (GND)

Power supply (+5V)

Enable signal for row 2 and 3 (2 nd

Not Connected controller)

Table 2: Character LCD pins with 2 Controller

5

BASICS OF LCD

DDRAM - Display Data RAM

Display data RAM (DDRAM) stores display data represented in 8-bit character codes. Its extended capacity is 80 X 8 bits, or 80 characters. The area in display data RAM (DDRAM) that is not used for display can be used as general data RAM. So whatever you send on the DDRAM is actually displayed on the LCD. For LCDs like 1x16, only 16 characters are visible, so whatever you write after 16 chars is written in DDRAM but is not visible to the user.

Figures below will show you the DDRAM addresses of 1 Line, 2 Line and 4 Line LCDs.

Figure 2: DDRAM Address for 1 Line LCD

Figure 3: DDRAM Address for 2 Line LCD

Figure 4: DDRAM Address for 4 Line LCD

CGROM - Character Generator ROM

Now you might be thinking that when you send an ascii value to DDRAM, how the character is displayed on LCD? so the answer is CGROM. The character generator ROM generates 5 x 8 dot or 5 x 10 dot character patterns from 8-bit character codes (see Figure 5 and Figure 6 for more details). It can generate 208 5 x 8 dot character patterns and 32 5 x 10 dot character patterns.

Userdefined character patterns are also available by mask-programmed ROM.

6

Figure 5: LCD characters code map for 5x8 dots

7

Figure 6: LCD characters code map for 5x10 dots

8

As you can see in both the code maps, the character code from 0x00 to 0x07 is occupied by the

CGRAM characters or the user defined characters. If user want to display the fourth custom character then the code to display it is 0x03 i.e. when user send 0x03 code to the LCD DDRAM then the fourth user created charater or patteren will be displayed on the LCD.

CGRAM - Character Generator RAM

As clear from the name, CGRAM area is used to create custom characters in LCD. In the character generator RAM, the user can rewrite character patterns by program. For 5 x 8 dots, eight character patterns can be written, and for 5 x 10 dots, four character patterns can be written.

Later in this tutorial i will explain how to use CGRAM area to make custom character and also making animations to give nice effects to your application.

BF - Busy Flag

Busy Flag is an status indicator flag for LCD. When we send a command or data to the LCD for processing, this flag is set (i.e BF =1) and as soon as the instruction is executed successfully this flag is cleared (BF = 0). This is helpful in producing and exact ammount of delay. for the LCD processing.

To read Busy Flag, the condition RS = 0 and R/W = 1 must be met and The MSB of the LCD data bus (D7) act as busy flag. When BF = 1 means LCD is busy and will not accept next command or data and BF = 0 means LCD is ready for the next command or data to process.

Instruction Register (IR) and Data Register (DR)

There are two 8-bit registers in HD44780 controller Instruction and Data register. Instruction register corresponds to the register where you send commands to LCD e.g LCD shift command,

LCD clear, LCD address etc. and Data register is used for storing data which is to be displayed on LCD. when send the enable signal of the LCD is asserted, the data on the pins is latched in to the data register and data is then moved automatically to the DDRAM and hence is displayed on the LCD.

Data Register is not only used for sending data to DDRAM but also for CGRAM, the address where you want to send the data, is decided by the instruction you send to LCD. We will discuss more on LCD instuction set further in this tutorial.

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LCD COMMANDS

Commands and Instruction set

Only the instruction register (IR) and the data register (DR) of the LCD can be controlled by the

MCU. Before starting the internal operation of the LCD, control information is temporarily stored into these registers to allow interfacing with various MCUs, which operate at different speeds, or various peripheral control devices. The internal operation of the LCD is determined by signals sent from the MCU. These signals, which include register selection signal (RS), read/write signal

(R/W), and the data bus (DB0 to DB7), make up the LCD instructions (Table 3). There are four categories of instructions that:

Designate LCD functions, such as display format, data length, etc.

Set internal RAM addresses

Perform data transfer with internal RAM

Perform miscellaneous functions

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Table 3: Command and Instruction set for LCD type HD44780

Although looking at the table you can make your own commands and test them. Below is a breif list of useful commands which are used frequently while working on the LCD.

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No. Instruction Hex Decimal

1 Function Set: 8-bit, 1 Line, 5x7 Dots

2 Function Set: 8-bit, 2 Line, 5x7 Dots

3 Function Set: 4-bit, 1 Line, 5x7 Dots

0x30

0x38

0x20

48

56

32

4 Function Set: 4-bit, 2 Line, 5x7 Dots

5 Entry Mode

6

Display off Cursor off

(clearing display without clearing DDRAM content)

7 Display on Cursor on

8 Display on Cursor off

9 Display on Cursor blinking

10 Shift entire display left

12 Shift entire display right

13 Move cursor left by one character

14 Move cursor right by one character

0x28

0x06

0x08

0x0E

0x0C

0x0F

0x18

0x1C

0x10

0x14

40

6

8

14

12

15

24

30

16

20

15 Clear Display (also clear DDRAM content) 0x01

16

Set DDRAM address or coursor position on display

0x80+add *

1

128+add *

17

Set CGRAM address or set pointer to

CGRAM location

0x40+add ** 64+add **

Table 4: Frequently used commands and instructions for LCD

* DDRAM address given in LCD basics section see Figure 2,3,4

** CGRAM address from 0x00 to 0x3F, 0x00 to 0x07 for char1 and so on..

The table above will help you while writing programs for LCD. But after you are done testing with the table 4, i recommend you to use table 3 to get more grip on working with LCD and trying your own commands. In the next section of the tutorial we will see the initialization with some of the coding examples in C as well as assembly.

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LCD INITIALIZATION

Before using the LCD for display purpose, LCD has to be initialized either by the internal reset circuit or sending set of commands to initialize the LCD. It is the user who has to decide whether an LCD has to be initialized by instructions or by internal reset circuit. we will dicuss both ways of initialization one by one.

Initialization by internal Reset Circuit

An internal reset circuit automatically initializes the HD44780U when the power is turned on.

The following instructions are executed during the initialization. The busy flag (BF) is kept in the busy state until the initialization ends (BF = 1). The busy state lasts for 10 ms after VCC rises to

4.5 V.

Display clear

Function set:

DL = 1; 8-bit interface data

N = 0; 1-line display

F = 0; 5 x 8 dot character font

Display on/off control:

D = 0; Display off

C = 0; Cursor off

B = 0; Blinking off

Entry mode set:

I/D = 1; Increment by 1

S = 0; No shift

Note: If the electrical characteristics conditions listed under the table Power Supply Conditions

Using Internal Reset Circuit are not met, the internal reset circuit will not operate normally and will fail to initialize the HD44780U. For such a case, initial-ization must be performed by the

MCU as explained in the section, Initializing by Instruction.

As mentioned in the Note, there are certain condtions that has to be met, if user want to use initialization by internal reset circuit. These conditions are shown in the Table 5 below.

Table 5: Power Supply condition for Internal Reset circuit

Figure 7 shows the test condition which are to be met for internal reset circuit to be active.

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Figure 7: Internal Power Supply reset

Now the problem with the internal reset circuit is, it is highly dependent on power supply, to meet this critical power supply conditions is not hard but are difficult to achive when you are making a simple application. So usually the second menthod i.e. Initialization by instruction is used and is recommended most of the time.

Initialization by instructions

Initializing LCD with instructions is really simple. Given below is a flowchart that describles the step to follow, to initialize the LCD.

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Figure 8: Flow chart for LCD initialization

As you can see from the flow chart, the LCD is initialized in the following sequence...

1) Send command 0x30 - Using 8-bit interface

2) Delay 20ms

3) Send command 0x30 - 8-bit interface

4) Delay 20ms

5) Send command 0x30 - 8-bit interface

6) Delay 20ms

7) Send Function set - see Table 4 for more information

8) Display Clear command

9) Set entry mode command - explained below

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The first 3 commands are usually not required but are recomended when you are using 4-bit interface. So you can program the LCD starting from step 7 when working with 8-bit interface.

Function set command depends on what kind of LCD you are using and what kind of interface you are using (see Table 4 in LCD Command section).

LCD Entry mode

From Table 3 in command section, you can see that the two bits decide the entry mode for LCD, these bits are: a) I/D - Increment/Decrement bit b) S - Display shift.

With these two bits we get four combinations of entry mode which are 0x04,0x05,0x06,0x07 (see table 3 in LCD Command section). So we get different results with these different entry modes.

Normally entry mode 0x06 is used which is No shift and auto incremement. I recommend you to try all the possible entry modes and see the results, I am sure you will be surprised.

Programming example for LCD Initialization

CODE: (ASM)

LCD_data equ P2

;LCD Data port

LCD_D7 equ P2 .

7

;LCD D7/Busy Flag

LCD_rs equ P1 .

0

;LCD Register Select

LCD_rw equ P1 .

1

;LCD Read/Write

LCD_en equ P1 .

2

;LCD Enable

LCD_init :

mov

LCD_data ,# 38H

;Function set: 2 Line, 8-bit, 5x7 dots

clr

LCD_rs

;Selected command register

clr

LCD_rw

;We are writing in instruction register

setb

LCD_en

;Enable H->L

clr

LCD_en

acall

LCD_busy

;Wait for LCD to process the command

mov

LCD_data ,# 0FH

;Display on, Curson blinking command

clr

LCD_rs

;Selected instruction register

clr

LCD_rw

;We are writing in instruction register

setb

LCD_en

;Enable H->L

clr

LCD_en

acall

LCD_busy

;Wait for LCD to process the command

mov

LCD_data ,# 01H

;Clear LCD

clr

LCD_rs

;Selected command register

clr

LCD_rw

;We are writing in instruction register

setb

LCD_en

;Enable H->L

clr

LCD_en

acall

LCD_busy

;Wait for LCD to process the command

mov

LCD_data ,# 06H

;Entry mode, auto increment with no shift

clr

LCD_rs

;Selected command register

clr

LCD_rw

;We are writing in instruction register

setb

LCD_en

;Enable H->L

clr

LCD_en

16

acall

LCD_busy

;Wait for LCD to process the command

ret

;Return from routine

Now we can do the same thing in C, I am giving example using Keil C. Similar code can be written for SDCC.

CODE: (C)

#include <AT89X51.H>.

#define LCD_data P2

#define LCD_D7 P2_7

#define LCD_rs P1_0

#define LCD_rw P1_1

#define LCD_en P1_2 void LCD_init ()

{

LCD_data = 0x38 ;

//Function set: 2 Line, 8-bit, 5x7 dots

LCD_rs = 0 ;

//Selected command register

LCD_rw = 0 ;

//We are writing in data register

LCD_en = 1 ;

//Enable H->L

LCD_en = 0 ;

LCD_busy () ;

//Wait for LCD to process the command

LCD_data = 0x0F ;

//Display on, Curson blinking command

LCD_rs = 0 ;

//Selected command register

LCD_rw = 0 ;

//We are writing in data register

LCD_en = 1 ;

//Enable H->L

LCD_en = 0 ;

LCD_busy () ;

//Wait for LCD to process the command

LCD_data = 0x01 ;

//Clear LCD

LCD_rs = 0 ;

//Selected command register

LCD_rw = 0 ;

//We are writing in data register

LCD_en = 1 ;

//Enable H->L

LCD_en = 0 ;

LCD_busy () ;

//Wait for LCD to process the command

LCD_data = 0x06 ;

//Entry mode, auto increment with no shift

LCD_rs = 0 ;

//Selected command register

LCD_rw = 0 ;

//We are writing in data register

LCD_en = 1 ;

//Enable H->L

LCD_busy () ;

}

With the help of the above code, you are able to initialize the LCD. Now there is a function/subroutine coming in the code i.e. LCD_busy, which is used to put delay for LCD so that there should not be any command or data sent to the LCD untill it finish executing the command. More on this delay routine is explained in the next section.

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CHECKING BUSY FLAG

Reading the busy Flag

As discussed in the previous section, there must be some delay which is needed to be there for

LCD to successfully process the command or data. So this delay can be made either with a delay loop of specified time more than that of LCD process time or we can read the busy flag, which is recomended. The reason to use busy flag is that delay produced is almost for the exact amount of time for which LCD need to process the time. So is best suited for every application.

Steps to read busy flag

When we send the command, the BF or D7th bit of the LCD becomes 1 and as soon as the command is processed the BF = 0. Following are the steps to be kept in mind while reading the

Busy flag.

Select command register

Select read operation

Send enable signal

Read the flag

So following the above steps we can write the code in assembly as below...

CODE:

;Ports used are same as the previous example

LCD_busy :

setb

LCD_D7

;Make D7th bit of LCD data port as i/p

setb

LCD_en

;Make port pin as o/p

clr

LCD_rs

;Select command register

setb

LCD_rw

;we are reading

check :

clr

LCD_en

;Enable H->L

setb

LCD_en

jb

LCD_D7 , check

;read busy flag again and again till it becomes

0

ret

;Return from busy routine

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

CODE:

void LCD_busy ()

{

LCD_D7 = 1 ;

//Make D7th bit of LCD as i/p

LCD_en = 1 ;

//Make port pin as o/p

LCD_rs = 0 ;

//Selected command register

LCD_rw = 1 ;

//We are reading

while ( LCD_D7 ){

//read busy flag again and again till it becomes

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0

LCD_en = 0 ;

//Enable H->L

LCD_en = 1 ;

}

}

The above routine will provide the necessary delay for the instructions to complete. If you dont want to read the busy flag you can simply use a delay routine to provide a specific amount of delay. A simple delay routine for the LCD is given below.

CODE:

LCD_busy_delay :

mov

r7 ,# 50H back :

mov

r6 ,# FFH

djnz

r6 , $

djnz

r7 , back

ret

;Return from busy routine

CODE:

void LCD_busy_delay ()

{ unsigned char i , j ; for ( i = 0 ; i < 50 ; i ++ )

//A simple for loop for delay

for ( j = 0 ; j < 255 ; j ++ ) ;

}

Now we are ready with the initialization routine and the busy routine for LCD. In the next section we will see how to send data and command to the LCD.

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SENDING COMMAND & DATA TO LCD

Sending Commands to LCD

To send commands we simply need to select the command register. Everything is same as we have done in the initialization routine. But we will summarize the common steps and put them in a single subroutine. Following are the steps:

Move data to LCD port select command register select write operation send enable signal wait for LCD to process the command

Keeping these steps in mind we can write LCD command routine as.

CODE:

;Ports used are same as the previous example

;Routine to send command to LCD

LCD_command :

mov

LCD_data , A

;Move the command to LCD port

clr

LCD_rs

;Selected command register

clr

LCD_rw

;We are writing in instruction register

setb

LCD_en

;Enable H->L

clr

LCD_en

acall

LCD_busy

;Wait for LCD to process the command

ret

;Return from busy routine

; Usage of the above routine

; A will carry the command for LCD

; e.g. we want to send clear LCD command

;

; mov a,#01H ;01H is command for clearing LCD

; acall LCD_command ;Send the command

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

CODE:

void LCD_command ( unsigned char var )

{

LCD_data = var ;

//Function set: 2 Line, 8-bit, 5x7 dots

LCD_rs = 0 ;

//Selected command register

LCD_rw = 0 ;

//We are writing in instruction register

LCD_en = 1 ;

//Enable H->L

LCD_en = 0 ;

LCD_busy () ;

//Wait for LCD to process the command

}

// Using the above function is really simple

// var will carry the command for LCD

// e.g.

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//

// LCD_command(0x01);

Setting cursor position on LCD

To set the cursor position on LCD, we need to send the DDRAM address...

C

ODE:

Bit7 6 5 4 3 2 1 0

1 AD6 AD5 AD4 AD3 AD2 AD1 AD0

The seventh bit is always 1, and bit 0 to 7 are DDRAM address (See the introduction section of

LCD). so if you want to put the cursor on first position the address will be '0000000B' in binary and 7th bit is 1. so address will be 0x80, so for DDRAM all address starts from 0x80.

For 2 line and 16 character LCD. The adress from 0x80 to 0x8F are visible on first line and 0xC0 to 0xCF is visible on second line, rest of the DDRAM area is still available but is not visible on the LCD, if you want to check this thing, then simply put a long sting greater than 16 character and shift the entire display, you will see all the missing character coming from the back.. this way you can make scrolling line on LCD (see more on shifting display in commands section ).

Below is an example for setting cursor position on LCD.

CODE:

;We are placing the cursor on the 4th position

;so the DDRAM address will be 0x03

;and the command will be 0x80+0x03 = 0x83

mov

a ,# 83H

;load the command

acall

LCD_command

;send command to LCD

CODE:

// to do the same thing is C

// as we done before

LCD_command ( 0x83 ) ;

Sending Data to LCD

To send data we simply need to select the data register. Everything is same as the command routine. Following are the steps:

Move data to LCD port select data register select write operation send enable signal

21

• wait for LCD to process the data

Keeping these steps in mind we can write LCD command routine as.

CODE:

;Ports used are same as the previous example

;Routine to send data (single character) to LCD

LCD_senddata :

mov

LCD_data , A

;Move the command to LCD port

setb

LCD_rs

;Selected data register

clr

LCD_rw

;We are writing

setb

LCD_en

;Enable H->L

clr

LCD_en

acall

LCD_busy

;Wait for LCD to process the data

ret

;Return from busy routine

; Usage of the above routine

; A will carry the character to display on LCD

; e.g. we want to print A on LCD

;

; mov a,#'A' ;Ascii value of 'A' will be loaded in accumulator

; acall LCD_senddata ;Send data

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

CODE:

void LCD_senddata ( unsigned char var )

{

LCD_data = var ;

//Function set: 2 Line, 8-bit, 5x7 dots

LCD_rs = 1 ;

//Selected data register

LCD_rw = 0 ;

//We are writing

LCD_en = 1 ;

//Enable H->L

LCD_en = 0 ;

LCD_busy () ;

//Wait for LCD to process the command

}

// Using the above function is really simple

// we will pass the character to display as argument to function

// e.g.

//

// LCD_senddata('A');

Now you have seen that its really easy to send command and data to LCD. Now what if we have a string to send to LCD? how we are going to do that?

Is simple, we will store the LCD string in the ROM of controller and call the string character by character. A simple exmple is shown below.

CODE:

22

;Sending string to LCD Example

LCD_sendstring :

clr

a

;clear Accumulator for any previous data

movc

a ,@ a + dptr

;load the first character in accumulator

jz

exit

;go to exit if zero

acall

lcd_senddata

;send first char

inc

dptr

;increment data pointer

sjmp

LCD_sendstring

;jump back to send the next character

exit

:

ret

;End of routine

; Usage of the above routine

; DPTR(data pointer) will carry the address

; of string to send to LCD.

; e.g. we want to print "LCD Tutorial" on LCD then

;

; mov dptr,#my_string ;my_string is the label where the string is stored

; acall LCD_sendstring ;Send string

;

; To store a string..

; my_string:

; DB "LCD Tutorial", 00H

; 00H indicate that string is finished.

The equivalent C code Keil C compiler. Similar code can be written for SDCC.

CODE:

void LCD_sendstring ( unsigned char * var )

{ while ( * var )

//till string ends

LCD_senddata ( * var ++ ) ;

//send characters one by one

}

// Using the above function is really simple

// we will pass the string directly to the function

// e.g.

//

// LCD_sendstring("LCD Tutorial");

Now we are ready with sending data and sending command to LCD. Now the last and final section which is creating custom characters or patterns to display on LCD. Please proceed to the next section to read more.

23

CREATING CUSTOM CHARACTERS

CGRAM and Character Building

As already explained, all character based LCD of type HD44780 has CGRAM area to create user defined patterns. For making custom patterns we need to write values to the CGRAM area defining which pixel to glow. These values are to be written in the CGRAM adress starting from

0x40. If you are wondering why it starts from 0x40? Then the answer is given below.

Bit 7 is 0 and Bit 6 is 1, due to which the CGRAM adress command starts from 0x40, where the address of CGRAM (Acg) starts from 0x00. CGRAM has a total of 64 Bytes. When you are using LCD as 5x8 dots in function set then you can define a total of 8 user defined patterns (1

Byte for each row and 8 rows for each pattern), where as when LCD is working in 5x10 dots, you can define 4 user defined patterns.

Lets take an of bulding a custom pattern. All we have to do is make a pixel-map of 7x5 and get the hex or decimal value or hex value for each row, bit value is 1 if pixel is glowing and bit value is 0 if pixel is off. The final 7 values are loaded to the CGRAM one by one. As i said there are 8 rows for each pattern, so last row is usually left blank (0x00) for the cursor. If you are not using cursor then you can make use of that 8th row also. so you get a bigger pattern.

To explain the above explaination in a better way. I am going to take an example. Lets make a

"Bell" pattern as shown below.

24

Now we get the values for each row as shown.

Bit: 4 3 2 1 0 - Hex

Row1: 0 0 1 0 0 - 0x04

Row2: 0 1 1 1 0 - 0x0E

Row3: 0 1 1 1 0 - 0x0E

Row4: 0 1 1 1 0 - 0x0E

Row5: 1 1 1 1 1 - 0x1F

Row6: 0 0 0 0 0 - 0x00

Row7: 0 0 1 0 0 - 0x04

Row8: 0 0 0 0 0 - 0x00

We are not using row 8 as in our pattern it is not required. if you are using cursor then it is recommended not to use the 8th row. Now as we have got the values. We just need to put these values in the CGRAM. You can decided which place you want to store in. Following is the memory map for custom patterns in CGRAM.

Memory Map

Pattern No. CGRAM Address (Acg)

1 0x00 - 0x07

5

6

7

2

3

4

0x08 - 0x0F

0x10 - 0x17

0x18 - 0x1F

0x20 - 0x27

0x28 - 0x2F

0x30 - 0x37

8 0x38 - 0x3F

We can point the cursor to CGRAM address by sending command, which is 0x40 + CGRAM address (For more information please see Table 4 in commands section ). Lets say we want to write the Bell pattern at second pattern location. So we send the command as 0x48 (0x40 +

0x08), and then we send the pattern data. Below is a small programming example to do this.

CODE:

;LCD Ports are same as discussed in previous sections

LCD_Build :

mov

A ,# 48H

;Load the location where we want to store

acall

LCD_command

;Send the command

mov

A ,# 04H

;Load row 1 data

acall

LCD_senddata

;Send the data

mov

A ,# 0EH

;Load row 2 data

acall

LCD_senddata

;Send the data

mov

A ,# 0EH

;Load row 3 data

acall

LCD_senddata

;Send the data

mov

A ,# 0EH

;Load row 4 data

25

acall

LCD_senddata

;Send the data

mov

A ,# 1FH

;Load row 5 data

acall

LCD_senddata

;Send the data

mov

A ,# 00H

;Load row 6 data

acall

LCD_senddata

;Send the data

mov

A ,# 04H

;Load row 7 data

acall

LCD_senddata

;Send the data

mov

A ,# 00H

;Load row 8 data

acall

LCD_senddata

;Send the data

ret

;Return from routine

The above routine will create bell character at pattern location 2. To display the above generated pattern on LCD, simply load the pattern location (0,1,2,...7) and call the LCD_senddata subroutine. Now we can also write the above routine in C as...

CODE:

// LCD Ports are same as discussed

in

previous sections void LCD_Build

(){

LCD_command

(

0x48

)

; //Load the location where we want to store

LCD_senddata

(

0x04

)

; //Load row 1 data

LCD_senddata

(

0x0E

)

; //Load row 2 data

LCD_senddata

(

0x0E

)

; //Load row 3 data

LCD_senddata

(

0x0E

)

; //Load row 4 data

LCD_senddata

(

0x1F

)

; //Load row 5 data

LCD_senddata

(

0x00

)

; //Load row 6 data

LCD_senddata

(

0x04

)

; //Load row 7 data

LCD_senddata

(

0x00

)

; //Load row 8 data

}

I think now most of you find programing in C more simple than assembly. We can also summarize the above in a simple small routine so that you can simply call the build routine providing a pointer to array containing the build data. Below example shows how to do it.

CODE:

// Input :

// location : location where you want to store

// 0 , 1 , 2 ,....

7

// ptr : Pointer to pattern data

//

// Usage :

// pattern

[

8

]

=

{

0x04 , 0x0E , 0x0E , 0x0E , 0x1F , 0x00 , 0x04 , 0x00

}

;

// LCD_build

(

1 , pattern

)

;

//

// LCD Ports are same as discussed

in

previous sections void LCD_build

(

unsigned char location , unsigned char *

ptr ){

unsigned char i

;

if

(

location < 8

){

LCD_command

(

0x40 +

(

location * 8

))

;

for

(

i= 0

;i<8;i++)

LCD_senddata

( ptr [

i

])

;

}

}

26

So the above example shows how to simpify most of your work. To make easy for you to find the values for custom patterns, you can make use of Custom Character Calculator given on web page.

This part of the tutorial ends here. For programming help please post in the

forum

. Have a nice time with your LCD.

27

INTRODUCTION TO USING LCD IN 4-BIT MODE

Till now whatever we discussed in the previous part of ths LCD tutorial, we were dealing with 8bit mode. Now we are going to learn how to use LCD in 4-bit mode. There are many reasons why sometime we prefer to use LCD in 4-bit mode instead of 8-bit. One basic reason is lesser number of pins are needed to interface LCD.

In 4-bit mode the data is sent in nibbles, first we send the higher nibble and then the lower nibble.

To enable the 4-bit mode of LCD, we need to follow special sequence of initialization that tells the LCD controller that user has selected 4-bit mode of operation. We call this special sequence as resetting the LCD. Following is the reset sequence of LCD.

ƒ

ƒ

ƒ

ƒ

ƒ

ƒ

ƒ

ƒ

ƒ

Wait for abour 20mS

Send the first init value (0x30)

Wait for about 10mS

Send second init value (0x30)

Wait for about 1mS

Send third init value (0x30)

Wait for 1mS

Select bus width (0x30 - for 8-bit and 0x20 for 4-bit)

Wait for 1mS

The busy flag will only be valid after the above reset sequence. Usually we do not use busy flag in 4-bit mode as we have to write code for reading two nibbles from the LCD. Instead we simply put a certain ammount of delay usually 300 to 600uS. This delay might vary depending on the

LCD you are using, as you might have a different crystal frequency on which LCD controller is running. So it actually depends on the LCD module you are using. So if you feel any problem running the LCD, simply try to increase the delay. This usually works. For me about 400uS works perfect.

LCD connections in 4-bit Mode

Below is the connection diagram of LCD in 4-bit mode, where we only need 6 pins to interface an LCD. D4-D7 are the data pins connection and Enable and Register select are for LCD control pins. We are not using Read/Write (RW) Pin of the LCD, as we are only writing on the LCD so we have made it grounded permanently. If you want to use it.. then you may connect it on your controller but that will only increase another pin and does not make any big difference.

Potentiometer RV1 is used to control the LCD contrast. The unwanted data pins of LCD i.e. D0-

D3 are connected to ground.

28

Sending data/command in 4-bit Mode

We will now look into the common steps to send data/command to LCD when working in 4-bit mode. As i already explained in 4-bit mode data is sent nibble by nibble, first we send higher nibble and then lower nibble. This means in both command and data sending function we need to saperate the higher 4-bits and lower 4-bits.

The common steps are:

ƒ

ƒ

ƒ

ƒ

ƒ

ƒ

Mask lower 4-bits

Send to the LCD port

Send enable signal

Mask higher 4-bits

Send to LCD port

Send enable signal

We are done with the theory part now, In the next section we will take a look at the programming microcontroller to control LCD in 4-bit mode.

4-bit Initialization

Initialization of LCD is completed only after the reset sequence and basic initialization

29

commands. We have already discussed about the reset sequence of the lcd in the previous section.

So lets look at the programming now...

Assembly Program

CODE:

;In this whole 4-bit tutorial LCD is connected to

;my controller in following way...

;D4 - P3.0

;D5 - P3.1

;D6 - P3.2

;D7 - P3.3

;EN - P3.7

;RS - P3.5

lcd_port equ P3

;LCD connected to Port3

en equ P3 .

7

;Enable connected to P3.7

rs equ P3 .

5

;Register select to P3.5

lcd_reset :

;LCD reset sequence

mov

lcd_port , # 0FFH

mov

delay ,# 20

;20mS delay

acall

delayms

mov

lcd_port , # 83H

;Data = 30H, EN = 1, First Init

mov

lcd_port , # 03H

;Data = 30H, EN = 0

mov

delay ,# 15

;Delay 15mS

acall

delayms

mov

lcd_port , # 83H

;Second Init, Data = 30H, EN = 1

mov

lcd_port , # 03H

;Data = 30H, EN = 0

mov

delay ,# 5

;Delay 5mS

acall

delayms

mov

lcd_port , # 83H

;Third Init

mov

lcd_port , # 03H

mov

delay ,# 5

;Delay 5mS

acall

delayms

mov

lcd_port , # 82H

;Select Data width (20H for 4bit)

mov

lcd_port , # 02H

;Data = 20H, EN = 0

mov

delay ,# 5

;Delay 5mS

acall

delayms

ret

lcd_init :

acall

lcd_reset

;Call LCD Reset sequence

mov

a ,# 28H

;4-bit, 2 line, 5x7 dots

acall

lcd_cmd

;Call LCD command

mov

a ,# 0CH

;Display ON cursor OFF

acall

lcd_cmd

;Call LCD command

mov

a ,# 06H

;Set entry mode (Auto increment)

acall

lcd_cmd

;Call LCD command

mov

a ,# 80H

;Bring cursor to line 1

acall

lcd_cmd

;Call LCD command

ret

C Program

30

CODE:

//The pins used are same as explained earlier

#define lcd_port P3

//LCD Registers addresses

#define LCD_EN 0x80

#define LCD_RS 0x20 void lcd_reset ()

{

lcd_port = 0xFF ;

delayms ( 20 ) ;

lcd_port = 0x03 + LCD_EN ;

lcd_port = 0x03 ;

delayms ( 10 ) ;

lcd_port = 0x03 + LCD_EN ;

lcd_port = 0x03 ;

delayms ( 1 ) ;

lcd_port = 0x03 + LCD_EN ;

lcd_port = 0x03 ;

delayms ( 1 ) ;

lcd_port = 0x02 + LCD_EN ;

lcd_port = 0x02 ;

delayms ( 1 ) ;

} void lcd_init ()

{

lcd_reset () ;

// Call LCD reset

lcd_cmd ( 0x28 ) ;

// 4-bit mode - 2 line - 5x7 font.

lcd_cmd ( 0x0C ) ;

// Display no cursor - no blink.

lcd_cmd ( 0x06 ) ;

// Automatic Increment - No Display shift.

lcd_cmd ( 0x80 ) ;

// Address DDRAM with 0 offset 80h.

}

Sending Dommand/Data to LCD in 4-bit mode

Assembly Program

CODE:

lcd_cmd :

;LCD command Routine

mov

temp , a

;Save a copy of command to temp

swap

a

;Swap to use higher nibble

anl

a ,# 0FH

;Mask the first four bits

add

a ,# 80H

;Enable = 1, RS = 0

mov

lcd_port , a

;Move it to lcd port

anl

a ,# 0FH

;Enable = 0, RS = 0

mov

lcd_port , a

;Move to lcd port

mov

a , temp

;Reload the command from temp

anl

a ,# 0FH

;Mask first four bits

add

a ,# 80H

;Enable = 1

31

mov

lcd_port , a

;Move to port

anl

a ,# 0FH

;Enable = 0

mov

lcd_port , a

;Move to lcd port

mov

delay ,# 1

;delay 1 ms

acall

delayms

ret

lcd_dat :

;LCD data Routine

mov

temp , a

;Keep copy of data in temp

swap

a

;We need higher nibble

anl

a ,# 0FH

;Mask first four bits

add

a ,# 0A0H

;Enable = 1, RS = 1

mov

lcd_port , a

;Move to lcd port

nop clr

en

;Enable = 0

mov

a , temp

;Reload the data from temp

anl

a ,# 0FH

;we need lower nibble now

add

a ,# 0A0H

;Enable = 1, RS = 1

mov

lcd_port , a

;Move to lcd port

nop clr

en

;Enable = 0

mov

delay ,# 1

;Delay 1mS

acall

delayms

ret

C Program

CODE:

void lcd_cmd ( char cmd )

{

lcd_port = (( cmd >> 4 ) & 0x0F ) | LCD_EN ;

lcd_port = (( cmd >> 4 ) & 0x0F ) ;

lcd_port = ( cmd & 0x0F ) | LCD_EN ;

lcd_port = ( cmd & 0x0F ) ;

delayus ( 200 ) ;

delayus ( 200 ) ;

} void lcd_data ( unsigned char dat )

{

lcd_port = ((( dat >> 4 ) & 0x0F ) | LCD_EN | LCD_RS ) ;

lcd_port = ((( dat >> 4 ) & 0x0F ) | LCD_RS ) ;

lcd_port = (( dat & 0x0F ) | LCD_EN | LCD_RS ) ;

lcd_port = (( dat & 0x0F ) | LCD_RS ) ;

delayus ( 200 ) ;

delayus ( 200 ) ;

}

32

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