I have written the following code to interface an LCD on 8051 using 4 bits. However, the code is not running. Please help.



U equ 31h ;memory location to hold upper nibble
L equ 32h ;memory location to hold lower nibble

Port equ P2 ;data port to connect LCD
EN equ P2.6 ;RS pin connection
RW equ P2.5 ;RW pin connection
RS equ P2.4 ;EN pin connection



ORG 0000h
LJMP MAIN

ORG 0100H

MAIN:
ACALL init

MOV A, #'H' ;
ACALL lcd_data ;in first line of LCD
MOV A, #'E'
ACALL lcd_data
MOV A, #'L'
ACALL lcd_data
MOV A, #'L'
ACALL lcd_data
MOV A, #'O '
ACALL lcd_data
MOV A, #''
ACALL lcd_data
MOV A, #'W'
ACALL lcd_data
MOV A, #'O'
ACALL lcd_data
MOV A, #'R'
ACALL lcd_data
MOV A, #'L'
ACALL lcd_data
MOV A, #'D'
ACALL lcd_data
L1: SJMP L1 ;INFINITE LONG LOOP



MASK:
MOV L,A ;save A at temp location L
ANL L,#00FH ;mask it with 0Fh
SWAP A ;swap nibble
ANL A,#00FH ;mask it with 0fh
MOV U,A ;save it at temp location U
RET ;return


;move to port subrotine
loop:
MOV Port,A ;put content of A to port
SETB EN ;make EN high
ACALL DELAY ;call a short delay routine
CLR EN ;clear EN
ACALL DELAY ;short delay
RET ;return


lcd_cmd:
CLR RW
CLR RS ;clear rs, going to send command
ACALL MASK ;separate the command and save to U and L
MOV A, U ;copy U to A
ACALL loop ;move content of a to port
MOV A, L ;copy L to A
ACALL loop ;move content of a to port
RET ;return



lcd_data:
CLR RW
SETB RS ;RS=1, going to send DATA
ACALL MASK ;separate the data and save to U & L
MOV A, U ;copy U to A
ACALL loop ;send it to LCD
MOV A, L ;copy L to A
ACALL loop ;send it to LCD
RET ;return



init:
ACALL delay ;some delay to lcd after power on
ACALL delay

MOV A, #20h ;send 20h to lcd to set 4 bit mode
CLR RS ;after that we can use lcd_cmd
SETB EN ;make EN switching
ACALL delay
CLR EN

MOV A, #20H
ACALL lcd_cmd
MOV A, #0CH; display on cursor off
ACALL lcd_cmd
MOV A, #06H;increment cursor
ACALL lcd_cmd
MOV A, #01H;clear display screen
ACALL lcd_cmd
RET

delay:
MOV R0, #30H
L2: MOV R1,#0FAH
L3: DJNZ R1, L3
DJNZ R0, L2
RET


end