LCD Information

LCD Interfacing with Microcontrollers tutorial 

►Introduction 

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

discuss about character based LCDs, their interfacing with various microcontrollers, various interfaces (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 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 characters, 

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 

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 RS 

Pin no. 5 R/W 

0 = Instruction input 

1 = Data input 

Pin no. 6 EN Enable signal 

0 = Write to LCD module 

1 = Read from LCD module 

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

Pin no. 8 D1 Data bus line 1 






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

Pin No. Name Description 

Table 1: Character LCD pins with 1 Controller 

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




Pin no. 5 D3 Data bus line 3



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

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

Pin no. 10 R/W 

Pin no. 11 RS 

0 = Write to LCD module 

1 = Read from LCD module 

0 = 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 (2 nd controller) 

Pin no. 16 NC Not Connected 

Table 2: Character LCD pins with 2 Controller 

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. 

►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 



►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. User defined character patterns are also available by mask-programmed ROM.

Figure 5: LCD characters code map for 5x8 dots

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 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 character or 

pattern 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 amount 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 instruction set further in this tutorial. 

►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 

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 brief 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 




5 Entry Mode 0x06 6 

6 

Display off Cursor off 

(clearing display without clearing DDRAM content) 

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* 

17 Set CGRAM address or set pointer to CGRAM location 0x40+add** 64+add** 

* 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.. 

Table 4: Frequently used commands and instructions for LCD 

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. 

►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 discuss 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, initialization must be performed by the MCU as explained in the section, 

Initializing by Instruction. 

As mentioned in the Note, there are certain conditions 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. 

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 method 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 describes the step to follow, to initialize the LCD.

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 

The first 3 commands are usually not required but are recommended 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 increment. 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: 

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, Curser blinking command 

clr LCD_rs ;Selected instruction register 





mov LCD_data,#01H ;Clear LCD 






mov LCD_data,#06H ;Entry mode, auto increment with no shift 






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 process the command 

LCD_data = 0x0F; //Display on, Curser blinking command 


LCD_rw = 0; //We are writing in data register

} 




LCD_data = 0x01; //Clear LCD 






LCD_data = 0x06; //Entry mode, auto increment with no shift 




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 until it finish executing the command. More on this delay routine is explained in 

the next section. 

►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 recommended. 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_rw = 1; //We are reading 

while(LCD_D7){ //read busy flag again and again till it becomes 

0 



} 

} 

The above routine will provide the necessary delay for the instructions to complete. If you don’t want to read the busy flag you can simply use a delay routine to 

provide the a specific amount of delay. A simple delay routine for the LCD is given below. 

CODE: 

LCD_busy: 

mov r7,#50H 

back: 

mov r6,#FFH 

djnz r6,$ 

djnz r7,back 


CODE: 

void LCD_busy() 

{ 

unsigned char i,j; 

for(i=0;i

LCD_command: 

mov LCD_data,A ;Move the command to LCD port 







; 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(unsigned char var) 

{ 

LCD_data = var; //Function set: 2 Line, 8-bit, 5x7 dots 


LCD_rw = 0; //We are writing in instruction register 




} 

// Using the above function is really simple 

// var will carry the command for LCD 

// e.g. 

// 

// LCD_command(0x01); 

Setting cursor position on LCD 

To 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 

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 

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 



acall LCD_busy ;Wait for LCD to process the data 



; 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(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 




}

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: 

;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 


; 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. 


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"); 

►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. 

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 

2 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). 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 






mov A,#1FH ;Load row 5 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(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 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

} 

} 

LCD_senddata(ptr[ i ]); 

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 below. 

Dec: 

Hex: 

Custom Character Calculator 

Bitmap Decimal Hex 

0, 0, 0, 0, 0, 0, 0, 0 

0 

0 

0 

0 

0 

0 

0 

0 

List of bitmap values: 

0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 

This part of the tutorial ends here. For programming help please post in the forum. Have a nice time with your LCD. 

►Introduction 

0 

0 

0 

0 

0 

0 

0 

0 

Till now whatever we discussed in the previous part of ths LCD tutorial, we were dealing with 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. 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. 

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 amount 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 

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 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. 

►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: 

Mask lower 4-bits 

Send to the LCD port 


Mask higher 4-bits 

Send to LCD port 


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 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 



acall delayms 

mov lcd_port, #83H ;Third Init 

mov lcd_port, #03H 


acall delayms 

mov lcd_port, #82H ;Select Data width (20H for 4bit) 



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 


mov a,#06H ;Set entry mode (Auto increment) 


mov a,#80H ;Bring cursor to line 1 


ret 

►C Program 

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); 



delayms(1); 



delayms(1); 



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 

mov lcd_port,a ;Move to port 

anl a,#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 

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

►C Program 

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 


nop 

clr en ;Enable = 0 


acall delayms 

ret 

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);

LCD Information

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