LCD Interfacing To 8051 in 8 bit mode

17 July 2011

3 min read

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Liquid Crystal Display also called as LCD is very helpful in providing user interface as well as for debugging purpose. The most common type of LCD controller is HITACHI 44780 which provides a simple interface between the controller & an LCD. These LCD's are very simple to interface with the controller as well as are cost effective.

The LCD requires 3 control lines (RS, R/W & EN) & 8 (or 4) data lines. The number on data lines depends on the mode of operation. If operated in 8-bit mode then 8 data lines plus 3 control lines i.e. total 11 lines are required. Here is a program for interfacing a LCD through 8051 in 8 bit mode.

The three control lines are RS, RW & Enable.

RS: Register Select. When RS = 0 the command register is selected. When RS=1 the data register is selected.

RW: Read or Write. When RW=0 write to LCD. When RW=1 read from LCD.

Enable: Used to Latch data into the LCD. A HIGH TO LOW edge latches the data into the LCD.

LCD Interfacing to 8051

In this program the controller checks the busy flag & waits till the LCD is busy.


LCD_RS	BIT	P2.5
LCD_RW	BIT	P2.6
CD_E	BIT	P2.7
LCD_pORT	EQU	P0

	ORG 0000h
	mov a,#38h call lcd_command mov a,#06h call lcd_command mov a,#0ch call lcd_command mov a,#01h call lcd_command mov a,#86h

	call lcd_command	//1st line 6th character
	mov a,#'D' call lcd_datadisplay mov a,#'N' call lcd_datadisplay mov a,#'A' call lcd_datadisplay mov a,#0c3h
	call lcd_command	//2nd Line 3rd character
	mov a,#'T' call lcd_datadisplay mov a,#'E' call lcd_datadisplay mov a,#'C' call lcd_datadisplay mov a,#'H' call lcd_datadisplay mov a,#'N' call lcd_datadisplay mov a,#'O' call lcd_datadisplay mov a,#'L' call lcd_datadisplay mov a,#'O' call lcd_datadisplay mov a,#'G' call lcd_datadisplay mov a,#'Y' call lcd_datadisplay
	/* Sends whatever data is in the Acc to the LCD as a Command */
	lcd_command:
	call lcd_ready	//waits till the LCD is ready
	mov LCD_PORT,a
	clr LCD_RW	//we are writing to LCD so RW=0
	clr LCD_RS	//Data we are sending is a command so RS=0
	setb LCD_E
	clr LCD_E	//LATCH data onto LCD
	ret
	/* Sends whatever data is in the Acc to the LCD to be displayed */
	lcd_datadisplay:
	call lcd_ready	//waits till the LCD is ready
	*mov LCD_PORT,a*
	*clr LCD_RW*	//we are writing to LCD so RW=0
	setb LCD_RS	//Data we are sending is a command so RS=0
	setb LCD_E
	clr LCD_E	//LATCH data onto LCD
	ret
	/* This subroutine checks the busy flag & waits till LCD is ready to ready for next instruction */
	lcd_ready:
	mov LCD_PORT,#0ffh clr LCD_RS
	setb LCD_RW	//we are reading from LCD so RW=1

	l1_lcd_ready:
	clr LCD_E setb LCD_E jb LCD_PORT.7, clr LCD_E ret END