| Written by Amol Shah, on Jul-2008 |
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1264  |
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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. In case of 4-bit mode only 4 data lines are required & the 8-bit data is sent by first sending the higher nibble followed by the lower nibble. Since we are operating the LCD in 4 bit mode only 7 port pins are required. Here is a program for interfacing a LCD through 8051 in 4 bit mode. The Higher 4 bits of P0 are connected to the higher 4 bits of the LCD i.e. P0.4 – P0.7 are connected to D4 – D7. 
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. · 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_RS BIT P2.5 LCD_RW BIT P2.6 LCD_E BIT P2.7 LCD_PORT EQU P0 //the higher nibble i.e. P0.4 - P0.7 is used ORG 0000h mov a,#20h call lcd_command mov a,#28h call lcd_command mov a,#06h call lcd_command mov a,#01h call lcd_command mov a,#0ch 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 loop: ajmp loop lcd_command: mov b,a call lcd_ready clr lcd_rw clr lcd_rs orl lcd_port,#0f0h mov a,b orl a,#0fh anl lcd_port,a setb lcd_e clr lcd_e orl lcd_port,#0f0h mov a,b swap a orl a,#0fh anl lcd_port,a setb lcd_e clr lcd_e ret lcd_datadisplay : mov b,a call lcd_ready clr lcd_rw setb lcd_rs orl lcd_port,#0f0h mov a,b orl a,#0fh anl lcd_port,a setb lcd_e clr lcd_e orl lcd_port,#0f0h mov a,b swap a orl a,#0fh anl lcd_port,a setb lcd_e clr lcd_e ret lcd_ready: clr lcd_e orl lcd_port,#0f0h clr lcd_rs setb lcd_rw setb lcd_e mov a,lcd_port clr lcd_e anl a,#0f0h mov temp,a orl lcd_port,#0f0h setb lcd_e mov a,lcd_port clr lcd_e anl a,#0f0h swap a orl a,temp jb acc.7,lcd_ready ret
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