PIC 4 bit 16x2 Hitachi LCD driver

by Stefan Johansson

Simple routines for controlling a HD44780 display. Useful if you are adding a display to an old project. The data bus and control lines can use any pin. It works just fine on pic 16f677 and 16f877.

Code:

Stefan Johansson shares this code:


;**********************************************************************
; Simple routines for controlling a HD44780 display                   *
; Useful if you are adding a display to an old project.               *
; The data bus and control lines can use any pin.                     *
; If the pin is open collector you need a pull up resistor            *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Filename:	    lcd.asm                                           *
;    Date:          20080204                                          *
;    File Version:  1.1                                               *
;                                                                     *
;    Author:        Stefan Johansson                                  *
;                   tessier at telia dot com                          *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Usage: #include 	<lcd.asm>                                     *
;			call	LCDINIT		; Initialize LCD      *
;                                                                     *
;			movlw	0x05                                  *
;			call	LCDADD		; Goto lcd adress 0x05*
;                                                                     *
;			movlw	'A'                                   *
;			call	LCDSEND		; Write character A   *
;**********************************************************************
;                                                                     *
;	Variables:	D0					      *
;			D1					      *
;			D2				              *
;			LCDTmp					      *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Notes: This was written and compiled for PIC 16f677.	      *
;           Modification might be needed for other models.	      *
;           Any comments, questions or improvements... mail me        *
;                                                                     *
;**********************************************************************


	; LCD control lines
	; Modify to match your project
	#define LCD_D4	PORTB, 3
	#define LCD_D5	PORTB, 2	; 4 data lines
	#define LCD_D6	PORTB, 1
	#define LCD_D7	PORTB, 0
	#define	LCD_RS	PORTB, 5	; 0 = Command, 1 = Data
	#define LCD_E	PORTB, 4	; 1 to send data


;*************************************************************
; Initialize LCD functions
;*************************************************************
LCDINIT
; Set correct TRIS values for LCD ports
	bsf 	STATUS, RP0 		;Bank 1
	bcf	LCD_RS
	bcf	LCD_E
	bcf	LCD_D4
	bcf	LCD_D5
	bcf	LCD_D6
	bcf	LCD_D7
	bcf	STATUS, RP0		;Bank 0

	movlw	0x40			; Initial delay, probably not needed...
	call	delay
	
	; Forced LCD initialization
	bcf	LCD_RS			; Set command mode
	bcf	LCD_E
	bsf	LCD_D4
	bsf	LCD_D5
	bcf	LCD_D6
	bcf	LCD_D7
	call	PULSE
	
	movlw	0x04
	call	delay
	
	call	PULSE	
	call	short_dly
	call	short_dly
	call	PULSE

	; Send the command to select 4-bit mode first
	bcf	LCD_D4
	call	PULSE

	; Function set
	; Format: xxxDNFxx		  D: 1= 8-bit, 0= 4-bit (use 4-bit!)
	movlw	b'00101000'		; N: 1= 2 lines, 0= 1 line
	call	LCDSEND			; F: 1= 5x10 font, 0= 5x8 font
	
	; Display control
	; Format: xxxxxDCB		  D: Display on(1)/0ff(0) 
	movlw	b'00001100'		; C: Cursor on(1)/0ff(0) 
	call	LCDSEND			; B: Blink on(1)/0ff(0) 
	
	; Entry mode set
	; Format: xxxxxxIS		  I: 1= Increment counter, 0= Decrement counter
	movlw	b'00000110'		; S: 1= "Accompanies display shift"
	call	LCDSEND

	; Cursor or display shift
	; Format: xxxxSRxx		  S: 1= Display shift, 0= Cursor move
	movlw	b'00010000'		; R: 1= Shift right, 0= Shift left
	call	LCDSEND

	movlw	b'00000001'		; Clear screen
	call	LCDSEND	

	bsf	LCD_RS		        ; Set data mode
	RETURN


;*************************************************************
; Moves "cursor"
;*************************************************************
LCDADD
	bcf	LCD_RS			; Command mode
	iorlw	0x80			; Goto DDRAM adress
	call	LCDSEND
	bsf	LCD_RS			; Data mode
	call	delay_1ms		; Takes a couple of ms
	RETURN


;*************************************************************
; Sends contens of W to display
;*************************************************************
LCDSEND	; Sends character in W to lcd. Does not alter RS line!
	movwf	LCDTmp
	bcf	LCD_D4
	bcf	LCD_D5
	bcf	LCD_D6
	bcf	LCD_D7

	btfsc	LCDTmp, 7
		bsf	LCD_D7
	btfsc	LCDTmp, 6
		bsf	LCD_D6
	btfsc	LCDTmp, 5
		bsf	LCD_D5
	btfsc	LCDTmp, 4
		bsf	LCD_D4
	call	PULSE


	bcf	LCD_D4
	bcf	LCD_D5
	bcf	LCD_D6
	bcf	LCD_D7

	btfsc	LCDTmp, 3
		bsf	LCD_D7
	btfsc	LCDTmp, 2
		bsf	LCD_D6
	btfsc	LCDTmp, 1
		bsf	LCD_D5
	btfsc	LCDTmp, 0
		bsf	LCD_D4
	call	PULSE

	return


;*************************************************************
; Pulse enable line
;*************************************************************
PULSE ; Pulse Enable.
	bsf	LCD_E
	nop				; Increase the delay here if you get
	nop				; problems with high clock speed
	nop				; Probably not needed since 
        nop				; 1 instruction @10MHz = 400ns
	bcf	LCD_E
	call	delay_1ms
	call	delay_1ms
	return


;*************************************************************
; Clears display
;*************************************************************
LCDCLR ; clears the entire display
	bcf	LCD_RS			; Set command mode
	movlw	b'00000001'		; Clear screen
	call	LCDSEND	
	bsf	LCD_RS			; Set data mode

	return


;*************************************************************
; Calls the delay_1ms W times
;*************************************************************
delay
	movwf	d0
dly_loop
	call	delay_1ms
	decfsz	d0, F
	goto	dly_loop
	return


;*************************************************************	
; 1ms delay.
; Modify this to match your processor speed.
; http://www.piclist.com/techref/piclist/codegen/delay.htm
;*************************************************************
delay_1ms
	movlw	0xF3		;2498 cycles
	movwf	d1
	movlw	0x02
	movwf	d2
Delay_0
	decfsz	d1, f
	goto	$+2
	decfsz	d2, f
	goto	Delay_0
	goto	$+1		;2 cycles
	return			;4 cycles (including call)


;*************************************************************	
; 40us delay.
; Modify this to match your processor speed.
; http://www.piclist.com/techref/piclist/codegen/delay.htm
;*************************************************************
short_dly
	movlw	0x1F		;94 cycles
	movwf	d1
short_dly_0
	decfsz	d1, f
	goto	short_dly_0
	goto	$+1		;2 cycles
	return			;4 cycles (including call)

Comments:

This is right:
; Format: xxxxSRxx S: 1= Display shift, 0= Cursor move
movlw b'00001000' ; R: 1= Shift right, 0= Shift left+

Works fine, just have to edit the beginning of the code to

#include <yourpic.pic>
call	LCDINIT		; Initialize LCD
movlw	0x05                                  
call	LCDADD		
movlw	'A'
call	LCDSEND		; Write character A   *
                                                              
;	Variables:
d0 equ 0x20					      
d1 equ 0x21
d2 equ 0x22				              
LCDTmp	equ 0x23

AND IT WORKS, thanks to the author.+

TakeThisOuTclemanTakeThisOuT at SPAMdrallim.com " I had include the PIC16F87X.inc file and define d0,d1,d2 and LCDTemp before it compiled."
this code DOES NOT WORK.
Stefan Johansson replies: But it works for me... Anyone else?
+
+

file: /Techref/io/lcd/lcd.asm.htm, 9KB, , updated: 2012/2/6 16:13, local time: 2025/4/5 21:22, owner: SJ-telia-G32,

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<A HREF="http://massmind.ecomorder.com/techref/io/lcd/lcd.asm.htm"> Simple routines for controlling a HD44780 display. Useful if you are adding a display to an old project. The data bus and control lines can use any pin. It works just fine on pic 16f677 and 16f877.</A>

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