Interfacing an LCD to the 8951 Microcontroller

Examples:

Here Data pins D0-D7 are connected to port1.0-port1.7 of 8951 microcontroller. Enable pin, RS are connected to P3.3 and P3.4 of 8951 respectively.

We can write program for LCD in two ways.

1. Sending commands and data to LVDs with a time delay.
2. Sending commands and data to LVDs with checking busy flag.

1. Program to display “ELECTROFRIENDS” in LCD without checking busy flag.

MOV A,#38H                           ; initialization LCD 2lines, 5×7 matrix.
ACALL COMMAND                   ; call command subroutine.
ACALL DELAY                          ; call delay subroutine.
MOV A,#0EH                           ; display on, cursor on
ACALL COMMAND
ACALL DELAY
MOV A,#01H                           ; Clear LCD
ACALL COMMAND
ACALL DELAY
MOV A,#06H                           ; shift cursor right
ACALL COMMAND
ACALL DELAY
MOV A,#80H                           ; cursor at beginning of 1st line
ACALL COMMAND
ACALL DELAY
MOV A,#’E’                             ; display letter E
ACALL DATA
ACALL DELAY
MOV A,#’L’                             ; display letter L
ACALL DATA
ACALL DELAY
MOV A,#’E’                             ; display letter E
ACALL DATA
ACALL DELAY
MOV A,#’C’                             ; display letter C
ACALL DATA
ACALL DELAY
MOV A,#’T’                             ; display letter T
ACALL DATA
ACALL DELAY
MOV A,#’R’                             ; display letter R
ACALL DATA
ACALL DELAY
MOV A,#’O’                             ; display letter O
ACALL DATA
ACALL DELAY
MOV A,#’F’                             ; display letter F
ACALL DATA
ACALL DELAY
MOV A,#’R’                             ; display letter R
ACALL DATA
ACALL DELAY
MOV A,#’I’                               ; display letter I
ACALL DATA
ACALL DELAY
MOV A,#’E’                             ; display letter E
ACALL DATA
ACALL DELAY
MOV A,#’N’                             ; display letter N
ACALL DATA
ACALL DELAY
MOV A,#’D’                             ; display letter D
ACALL DATA
ACALL DELAY
MOV A,#’S’                             ; display letter S
ACALL DATA
ACALL DELAY
HERE:  JMP HERE

COMMAND:   MOV P1,A        ; Send command to LCD
CLR P3.4          ; RS=0 for command
CLR P3.5          ; R/W=0 for write
SETB P3.3        ; E=1 for high pulse
CLR P3.3          ; E=0 for H-to-L pulse
RET

DATA:          MOV P1,A        ; Write data to LCD
SETB P3.4        ; RS=1 for data
CLR P3.5          ; R/W=0 for write
SETB P3.3        ; E=1 for high pulse
CLR P3.3          ; E=0 for H-to-L pulse
RET

DELAY:        MOV R2,#50
D1:              MOV R3,#0FFH
D2:              DJNZ R3,D2
DJNZ R2,D1
RET

2. Program to display “ELECTROFRIENDS” in LCD with checking busy flag.

MOV A,#38H                           ; initialization LCD 2lines, 5×7 matrix.
ACALL COMMAND                   ; call command subroutine.
MOV A,#0EH                           ; display on, cursor on
ACALL COMMAND
MOV A,#01H                           ; Clear LCD
ACALL COMMAND
MOV A,#06H                           ; shift cursor right
ACALL COMMAND
MOV A,#80H                           ; cursor at beginning of 1st line
ACALL COMMAND
MOV A,#’E’                             ; display letter E
ACALL DATA
MOV A,#’L’                             ; display letter L
ACALL DATA
MOV A,#’E’                             ; display letter E
ACALL DATA
MOV A,#’C’                             ; display letter C
ACALL DATA
MOV A,#’T’                             ; display letter T
ACALL DATA
MOV A,#’R’                             ; display letter R
ACALL DATA
MOV A,#’O’                             ; display letter O
ACALL DATA
MOV A,#’F’                             ; display letter F
ACALL DATA
MOV A,#’R’                             ; display letter R
ACALL DATA
MOV A,#’I’                             ; display letter I
ACALL DATA
MOV A,#’E’                             ; display letter E
ACALL DATA
MOV A,#’N’                             ; display letter N
ACALL DATA
MOV A,#’D’                             ; display letter D
ACALL DATA
MOV A,#’S’                             ; display letter S
ACALL DATA

HERE:  JMP HERE

COMMAND:   CALL READY     ; check whether LCD is ready
MOV P1,A          ; Send command to LCD
CLR P3.4           ; RS=0 for command
CLR P3.5           ; R/W=0 for write
SETB P3.3         ; E=1 for high pulse
CLR P3.3           ; E=0 for H-to-L pulse
RET

DATA:           CALL READY    ; check whether LCD is ready
MOV P1,A        ; Write data to LCD
SETB P3.4        ; RS=1 for data
CLR P3.5          ; R/W=0 for write
SETB P3.3        ; E=1 for high pulse
CLR P3.3          ; E=0 for H-to-L pulse
RET

READY:          SETB P1.7        ; make P1.7 input port
CLR P3.4          ; RS=0
SETB P3.5        ; R/W=0 for read
UP:                 SETB P3.3        ; E=1 for high pulse
CLR P3.3          ; E=0 for H-to-L pulse
JB P1.7, UP       ; stay until LCD is busy
RET