lcd interfacing with microcontrollers tutorial

8/2/2019 LCD Interfacing With Microcontrollers Tutorial

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LCD interfacing with Microcontrollers tutorial

IntroductionThe most commonly used Character based LCDs are based on Hitachi's HD44780controller or other which are compatible with HD44580. In this tutorial, we will discuss

about character based LCDs, their interfacing with various microcontrollers, variousinterfaces (8-bit/4-bit), programming, special stuff and tricks you can do with these

simple looking LCDs which can give a new look to your application.

For Specs and technical information HD44780 controller Click Here

Pin DescriptionThe 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 LCDssupporting 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 (twopins 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

Pin No. Name Description

Pin no. 1 VSS Power supply (GND)

Pin no. 2 VCC Power supply (+5V)

Pin no. 3 VEE Contrast adjust

Pin no. 4 RS0 = Instruction input

1 = Data input

Pin no. 5 R/W 0 = Write to LCD module


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1 = Read from LCD module

Pin no. 6 EN Enable signal

Pin no. 7 D0 Data bus line 0 (LSB)

Pin no. 8 D1 Data bus line 1

Pin no. 9 D2 Data bus line 2Pin no. 10 D3 Data bus line 3




Pin no. 14 D7 Data bus line 7 (MSB)

Table 1: Character LCD pins with 1 Control ler

Pin No. Name Description

Pin no. 1 D7 Data bus line 7 (MSB)







Pin no. 8 D0 Data bus line 0 (LSB)

Pin no. 9 EN1 Enable signal for row 0 and 1 (1stcontroller)

Pin no. 10 R/W 0 = Write to LCD module1 = Read from LCD module

Pin no. 11 RS0 = Instruction input

1 = Data input

Pin no. 12 VEE Contrast adjust

Pin no. 13 VSS Power supply (GND)

Pin no. 14 VCC Power supply (+5V)

Pin no. 15 EN2 Enable signal for row 2 and 3 (2nd

controller)

Pin no. 16 NC Not Connected

Table 2: Character LCD pins with 2 Control ler

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, theoperation and everything else is same for the double controller too. Lets take a look at the

basic information which is there in every LCD.


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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 16characters 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



CGROM - Character Generator ROMNow 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 ROMgenerates 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 5x 10 dot character patterns. Userdefined character patterns are also available by mask-

programmed ROM.


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Figure 5: LCD characters code map for 5x8 dots


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Figure 6: LCD characters code map for 5x10 dots

As you can see in both the code maps, the character code from 0x00 to 0x07 is occupiedby 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 codeto the LCD DDRAM then the fourth user created charater or patteren will be displayed

on the LCD.

CGRAM - Character Generator RAMAs 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 8dots, 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 makecustom character and also making animations to give nice effects to your application.


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BF - Busy FlagBusy 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 executedsuccessfully 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 theLCD 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 ordata 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.gLCD shift command, LCD clear, LCD address etc. and Data register is used for storingdata 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 movedautomatically 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, theaddress 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.

Commands and Instruction setOnly the instruction register (IR) and the data register (DR) of the LCD can be controlledby the MCU. Before starting the internal operation of the LCD, control information is

temporarily stored into these registers to allow interfacing with various MCUs, whichoperate 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 includeregister 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.

No.Instruction Hex Decimal

1 Function Set: 8-bit, 1 Line, 5x7 Dots 0x30 48




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5 Entry Mode 0x06 6

6

Display off Cursor off

(clearing display without clearing DDRAMcontent)

0x08 8

7 Display on Cursor on 0x0E 14

8 Display on Cursor off 0x0C 12

9 Display on Cursor blinking 0x0F 15

10 Shift entire display left 0x18 24

12 Shift entire display right 0x1C 30

13 Move cursor left by one character 0x10 16

14 Move cursor right by one character 0x14 20

15 Clear Display (also clear DDRAM content) 0x01 1

16

Set DDRAM address or coursor position on

display 0x80+add* 128+add*

17Set CGRAM address or set pointer toCGRAM location

0x40+add** 64+add**

Table 4: Frequently used commands and instruct ions 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 donetesting 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 theinitialization with some of the coding examples in C as well as assembly.

LCD InitializationBefore using the LCD for display purpose, LCD has to be initialized either by the internalreset 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. wewill dicuss both ways of initialization one by one.

Initialization by internal Reset Circuit

An internal reset circuit automatically initializes the HD44780U when the power isturned 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


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Function set:DL = 1; 8-bit interface data

N = 0; 1-line displayF = 0; 5 x 8 dot character font

Display on/off control:

D = 0; Display offC = 0; Cursor offB = 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 notoperate 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 touse 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 beactive.


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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 whenyou 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 thatdescribles 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 20ms3) Send command 0x30 - 8-bit interface

4) Delay 20ms5) Send command 0x30 - 8-bit interface

6) Delay 20ms7) Send Function set - see Table 4 for more information

8) Display Clear command9) Set entry mode command - explained below

The first 3 commands are usually not required but are recomended when you are using 4-


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bit interface. So you can program the LCD starting from step 7 when working with 8-bitinterface. 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 modefor 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 resultswith 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 theresults, I am sure you will be surprised.

Programming example for LCD Initialization

CODE:LCD_data equP2 ;LCD Data port

LCD_D7 equP2.7 ;LCD D7/Busy Flag

LCD_rs equP1.0 ;LCD Register Select

LCD_rw equP1.1 ;LCD Read/Write

LCD_en equP1.2 ;LCD Enable

LCD_init:

mov LCD_data,#38H ;Function set: 2 Line, 8-bit,

5x7 dots

clr LCD_rs ;Selected command registerclr 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 ininstruction register


clr LCD_en


command

mov LCD_data,#01H ;Clear LCD

clr LCD_rs ;Selected command register


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clr LCD_rw ;We are writing in



clr LCD_en


command

mov LCD_data,#06H ;Entry mode, auto increment

with no shift





clr LCD_en


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:#include .

#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 processthe command

LCD_data =0x0F; //Display on, Curson

blinking command


LCD_rw =0; //We are writing in data

register


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LCD_en =0;

LCD_busy(); //Wait for LCD to process

the command

LCD_data =0x01; //Clear LCD

LCD_rs =0; //Selected command registerLCD_rw =0; //We are writing in data

register


LCD_en =0;


the command

LCD_data =0x06; //Entry mode, auto

increment with no shift


LCD_rw =0; //We are writing in dataregister


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.

Reading the busy FlagAs 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 madeeither 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 delayproduced 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


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command is processed the BF = 0. Following are the steps to be kept in mind whilereading 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_rw =1; //We are reading

while(LCD_D7){ //read busy flag again and

again till it becomes 0LCD_en =0; //Enable H->L

LCD_en =1;

}

}

The above routine will provide the necessary delay for the instructions to complete. If


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you dont want to read the busy flag you can simply use a delay routine to provide the aspecific ammount of delay. A simple delay routine for the LCD is given below.

CODE:LCD_busy:

mov r7,#50Hback:

mov r6,#FFH

djnzr6,$

djnzr7,back

ret ;Return from busy

routine

CODE:void LCD_busy()

{

unsignedchar i,j;

for(i=0;i


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;Routine to send command to LCD

LCD_command:

mov LCD_data,A ;Move the command to LCD port





clr LCD_en


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


CODE:void LCD_command(unsignedchar var)

{

LCD_data = var; //Function set: 2 Line, 8-

bit, 5x7 dots


LCD_rw =0; //We are writing in



LCD_en =0;


the command

}

// Using the above function is really simple

// var will carry the command for LCD

// e.g.

//

// LCD_command(0x01);


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

CODE: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

mova,#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 LCDTo send data we simply need to select the data register. Everything is same as

the command routine. Following are the steps:


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Move data to LCD port

select data register

select write operation

send enable signal

wait for LCD to process the data

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


;Routine to send data (single character) to LCD

LCD_senddata:

mov LCD_data,A ;Move the command toLCD port

setb LCD_rs ;Selected data register

clr LCD_rw ;We are writing


clr LCD_en

acall LCD_busy ;Wait for LCD to

process the data

ret ;Return from busy

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


CODE:void LCD_senddata(unsignedchar var)

{

LCD_data = var; //Function set: 2 Line, 8-

bit, 5x7 dots


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LCD_rs =1; //Selected data register

LCD_rw =0; //We are writing


LCD_en =0;


the command}


// 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. Nowwhat 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:;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 characterexit:

ret ;End of routine


; DPTR(data pointer) will carry the address

; of string to send to LCD.


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; 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.


CODE:

void LCD_sendstring(unsignedchar*var){

while(*var) //till string ends

LCD_senddata(*var++); //send characters one

by one

}


// 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.

CGRAM and Character BuildingAs 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 theCGRAM 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? Thenthe answer is given below.


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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 LCDis 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 isglowing 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.

Now we get the values for each row as shown.

Bit: 4 3 2 1 0 - Hex

Row1: 0 0 1 0 0 - 0x04Row2: 0 1 1 1 0 - 0x0E

Row3: 0 1 1 1 0 - 0x0ERow4: 0 1 1 1 0 - 0x0E

Row5: 1 1 1 1 1 - 0x1FRow6: 0 0 0 0 0 - 0x00

Row7: 0 0 1 0 0 - 0x04Row8: 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


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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 - 0x072 0x08 - 0x0F

3 0x10 - 0x17

4 0x18 - 0x1F

5 0x20 - 0x27

6 0x28 - 0x2F

7 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). Letssay 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 programmingexample 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 storeacall 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






mov A,#1FH ;Load row 5 data








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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 theLCD_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 dataLCD_senddata(0x0E); //Load row 3 data

LCD_senddata(0x0E); //Load row 4 data

LCD_senddata(0x1F); //Load row 5 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 buildroutine 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


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void LCD_build(unsigned char location, unsigned char

*ptr){

unsigned char i;

if(location


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IntroductionTill now whatever we discussed in the previous part of ths LCD tutorial, we were dealingwith 8-bit 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. Onebasic 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 ofinitialization 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 ofLCD.

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 mightvary depending on the LCD you are using, as you might have a different crystalfrequency 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 toincrease the delay. This usually works. For me about 400uS works perfect.

LCD connections in 4-bit Mode


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Above 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 arefor 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. Theunwanted data pins of LCD i.e. D0-D3 are connected to ground.

Sending data/command in 4-bit ModeWe 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 wesend 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:

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 theprogramming microcontroller to control LCD in 4-bit mode.


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LCD interfacing with Microcontrollers tutorial - 4-bit Mode

4-bit InitializationInitialization of LCD is completed only after the reset sequence and basic initializationcommands. We have already discussed about the reset sequence of the lcd in the previous

section. So lets look at the programming now...

Assembly ProgramCODE:;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 equP3 ;LCD connected to Port3

en equP3.7 ;Enable connected to P3.7

rs equP3.5 ;Register select to P3.5

lcd_reset: ;LCD reset sequence

mov lcd_port,#0FFHmov 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 delay,#5 ;Delay 5mSacall delayms

mov lcd_port,#83H ;Third Init

mov lcd_port,#03H


acall delayms

mov lcd_port,#82H ;Select Data width (20H for

4bit)


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acall delayms

ret

lcd_init:

acall lcd_reset ;Call LCD Reset sequence

mova,#28H ;4-bit, 2 line, 5x7 dots

acall lcd_cmd ;Call LCD command

mova,#0CH ;Display ON cursor OFF


mova,#06H ;Set entry mode (Auto

increment)


mova,#80H ;Bring cursor to line 1


ret

C ProgramCODE://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;delayms(1);


lcd_port =0x03;

delayms(1);


lcd_port =0x02;

delayms(1);


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}

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 ProgramCODE:lcd_cmd: ;LCD command Routine

mov temp,a ;Save a copy of command to

temp

swapa ;Swap to use higher nibble

anla,#0FH ;Mask the first four bits

adda,#80H ;Enable = 1, RS = 0mov lcd_port,a ;Move it to lcd port

anla,#0FH ;Enable = 0, RS = 0

mov lcd_port,a ;Move to lcd port

mova,temp ;Reload the command from temp

anla,#0FH ;Mask first four bits

adda,#80H ;Enable = 1

mov lcd_port,a ;Move to port

anla,#0FH ;Enable = 0


mov delay,#1 ;delay 1 ms

acall delayms

ret

lcd_dat: ;LCD data Routine

mov temp,a ;Keep copy of data in temp

swapa ;We need higher nibble


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anla,#0FH ;Mask first four bits

adda,#0A0H ;Enable = 1, RS = 1


nop

clr en ;Enable = 0

mova,temp ;Reload the data from temp

anla,#0FH ;we need lower nibble now

adda,#0A0H ;Enable = 1, RS = 1


nop

clr en ;Enable = 0


acall delayms

ret

C ProgramCODE: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 (unsignedchar 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);

}

lcd interfacing with microcontrollers tutorial

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