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 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
Pin Number | Name | Description |
1 | VSS | Power supply (GND) |
2 | VCC | Power supply (+5V) |
3 | VEE | Contrast adjust |
4 | RS | 0 = Instruction input, 1 = Data input |
5 | R/W | 0 = Write to LCD module, 1 = Read from LCD module |
6 | EN | Enable signal |
7 | D0 | Data bus line 0 (LSB) |
8 | D1 | Data bus line 1 |
9 | D2 | Data bus line 2 |
10 | D3 | Data bus line 3 |
11 | D4 | Data bus line 4 |
12 | D5 | Data bus line 5 |
13 | D6 | Data bus line 6 |
14 | D7 | Data bus line 7 (MSB) |
Pin Number | Name | Description |
1 | D7 | Data bus line 7 (MSB) |
2 | D6 | Data bus line 6 |
3 | D5 | Data bus line 5 |
4 | D4 | Data bus line 4 |
5 | D3 | Data bus line 3 |
6 | D2 | Data bus line 2 |
7 | D1 | Data bus line 1 |
8 | D0 | Data bus line 0 (LSB) |
9 | EN1 | Enable signal for row 0 and 1 (1stcontroller) |
10 | R/W | 0 = Write to LCD module, 1 = Read from LCD module |
11 | RS | 0 = Instruction input, 1 = Data input |
12 | VEE | Contrast adjust |
13 | VSS | Power supply (GND) |
14 | VCC | Power supply (+5V) |
15 | EN2 | Enable signal for row 2 and 3 (2ndcontroller) |
16 | NC | Not Connected |
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
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. 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 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 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
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.
Number | Instruction | Hex | Decimal |
1 | Function Set: 8-bit, 1 Line, 5x7 Dots | 0x30 | 48 |
2 | Function Set: 8-bit, 2 Line, 5x7 Dots | 0x38 | 56 |
3 | Function Set: 4-bit, 1 Line, 5x7 Dots | 0x20 | 32 |
4 | Function Set: 4-bit, 2 Line, 5x7 Dots | 0x28 | 40 |
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..
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 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
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.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.
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 achieve 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...
- Send command 0x30 - Using 8-bit interface
- Delay 20ms
- Send command 0x30 - 8-bit interface
- Delay 20ms
- Send command 0x30 - 8-bit interface
- Delay 20ms
- Send Function set - see Table 4 for more information
- Display Clear command
- Set entry mode command - explained below
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
ASM Code
Code: Select all
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
acall LCD_busy ;Wait for LCD to process the command
ret ;Return from routine
Code: Select all
#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();
}
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 D7 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
ASM Code
Code: Select all
;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
Code: Select all
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 0
LCD_en = 0; //Enable H->L
LCD_en = 1;
}
}
ASM Code
Code: Select all
LCD_busy:
mov r7,#50H
back:
mov r6,#FFH
djnz r6,$
djnz r7,back
ret ;Return from busy routine
Code: Select all
void LCD_busy()
{
unsigned char i,j;
for(i=0;i<50;i++) //A simple for loop for delay
for(j=0;j<255;j++);
}
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
ASM Code
Code: Select all
;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
Code: Select all
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.
//
// LCD_command(0x01);
To set the cursor position on LCD, we need to send the DDRAM address...
Bit7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
1 | AD6 | AD5 | AD4 | AD3 | AD2 | AD1 | AD0 |
For 2 line and 16 character LCD. The address 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.
ASM Code
Code: Select all
;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: Select all
// to do the same thing is C
// as we done before
LCD_command(0x83);
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
ASM Code
Code: Select all
;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
Code: Select all
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');
Is simple, we will store the LCD string in the ROM of controller and call the string character by character. A simple example is shown below.
ASM Code
Code: Select all
;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.
Code: Select all
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 address 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 address 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 building 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 explanation 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 |
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 |
ASM Code
Code: Select all
;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
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
C Code
Code: Select all
//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
}
Code: Select all
//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 ]);
}
}
LCD in 4-bit Mode - Introduction
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
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 separate 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
LCD in 4-bit Mode - Programming
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...
ASM Code
Code: Select all
;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
Code: Select all
//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.
}
ASM Code
Code: Select all
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 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
Code: Select all
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);
}