LCD Interface with 89C51 & C

Introduction:

Over the winter break of 2020-2021, I did a project where I implemented an interface between 89C51 and the LCD module DMC-20481NY. The C and assembly code were written in MIDE-51. I sent ASCII from 89C51 to the LCD controller and the characters are displayed on the LCD display.

In C language, I created a new putchar() and made the printf() work with the control ASCII \n and \r in the LCD module.

Front View of Board

Back View of Board (Wiring)

Material List

Wire Wrap and Tool
74LS08 and 74LS02
LCD Module
DMC-20481NY
5V Power Supply
89C51 boot51 system (Created in previous project)
POT 10K ohm (VR)

The interface is a logic circuit that converts 89C51 write/read timing of WR, RD, and the address decoder output to the timing that the LCD required. The LCD interface, DMC 20481NY, is depicted above. The map of the LCD register into 89C51 memory location is shown in the table below.

The diagrams below were drawn by yours truly. They helped a lot with the wiring process. The first diagram is the IF diagram while the second one is a zoomed-out system diagram.

The complete wiring schematic and pin assignment chart are shown below.

ASM Code (click)

org 0000

start: Mov A,#30H

lcall sendCmd

Mov A,#0EH

lcall sendCmd

Mov A,#06H

lcall sendCmd

lcall clrScreen

mov dptr,#h2

lcall puts

sjmp $

delay: mov r7,#10h ; speed of LCD display

dll: mov r6,#0

djnz r6,$

djnz r7,dll

ret

sendCmd:

mov dptr,#cmdWr

movx @dptr,A

lcall delay

ret

putchar: mov dptr,#datWr ;LCD data register address is loaded to dptr

movx @dptr, a ;send the letter to LCD data register

lcall delay ;wait for busy =0,

ret

puts:

loop3: movx a,@dptr

jz return1

inc dptr

mov r1,dpl

mov r2, dph

lcall putchar

mov dpl,r1

mov dph, r2

sjmp loop3

return1: ret

clrScreen: mov a,#01h ;clear screen

lcall sendCmd

ret

org 1000h

buf: db "LCD test Code" ; what LCD will display.

count: db 13 ; number of letters from buf "LCD test Code"

hl: db 17

h2: db "LCD_test ASM V1.0",00h

cmdWr equ 8000h

datWr equ 8002H

end

C Language Code (click)

// Compile this code with SDCC 4.0

#include <8052.h>

#include <stdio.h>

static __xdata unsigned char *cmdWr;

static __xdata unsigned char *datWr;

void delay(void)

{ int i;

for (i=0;i<500;i++)

{}

}

void InitSerialPort(void)

{

SCON = 0x50; /* SCON: mode 1, 8-bit UART, enable rcvr */

TMOD |= 0x20; /* TMOD: timer 1, mode 2, 8-bit reload */

TH1 = 0xf3; /*TH1=0xf3; reload value for 2400 baud @ 12MHz*/

PCON=0x80; /* Smod1=1 related to 4800, 12MMHz*/

TR1 = 1; /* TR1: timer 1 start to run */

TI = 1; /* TI: set TI to send first char of UART */

}

int getchar()

{ while (!RI); /* assumes UART is initialized */

RI = 0;

return SBUF;

}

int putchar (int c)

{

*datWr=(char)c;

delay();

while (!TI); /* assumes UART is initialized */

TI = 0;

SBUF = c;

return c;

}

void gets(char *str)

{ while(1)

{ *str=(char)getchar();

if ((*str=='\n')||(*str=='\r')) break;

putchar(*str);

str++;

}

void LCDinit(void)

{ cmdWr= (__xdata unsigned char *)0x8000;

datWr= (__xdata unsigned char *)0x8002;

*cmdWr=0x01; //clear screen

delay();

*cmdWr=0x30;

delay();

*cmdWr=0x0e;

delay();

*cmdWr=0x06;

delay();

}

void main(void)

{

InitSerialPort();

LCDinit();

printf_tiny("LCD_test with C V1.0");

while (1)

{

}

C Language Board Display

ASM Code board display

Conclusion

In summation, I wrote and tested an LCD code in both ASM and C language. I used DMC20481NY LCD for the project. I tested these two codes multiple times and troubleshooted (trouble-shot?) all the errors. The entire project took me like 23 hours to complete, which is like a full day of nonstop work.