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Have I Corrupted My LCD Display?

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Hello,

I am playing with an LCD display for the first time and suspect that somehow its' character memory has been corrupted by yours truly.

Initially I had a go at getting the display working by myself but couldn't so then had a look at Nigels' tutorial (thanks Nigel - they really are useful for beginners like me). I modded the code a little; stripped out irrelevent bits and used 8 bit rather than 4 bit mode. However, now that it 'works' I see most of the characters are not as they should be; in the first pic it should display 'Hello / ready...' and in the second the whole alphabet capitalised.

Did I corrupt the character memory (CGRAM) when I first fiddled - is that possible? Can I rectify it and how?

Thanks in advance for any help.

7998-LCD%20Display%20001r.jpg


7999-LCD%20Displayr.jpg


Code:
;A project to drive a 16 x 2 LCD alphanumeric module (Powertip PC1602 from Rapid Electronics). 11 June 2009
;Most of this code is copied from Nigel Goodwins' tutorial. I've used 8 bit mode rather than 4 bit.

    list      p=16F690			
	#include <p16F690.inc>
	errorlevel  -302            ; suppress message 302 from list file
	errorlevel  -305

		__config (_INTRC_OSC_NOCLKOUT &_WDT_OFF &_PWRTE_OFF &_CP_OFF &_BOR_OFF &_IESO_OFF &_FCMEN_OFF &_MCLRE_OFF)
		

INT_VAR     	    UDATA 0x20

count       RES 1   
count1      RES 1
counta      RES 1
countb      RES 1   

#define     LCD_PORT    PORTC
#define     LCD_RS      PORTB,4
#define     LCD_E       PORTB,5

    org 0
;____________________________________________________________________________________________________________________ 
    
Start: 
    banksel ANSEL
    
    clrf    ANSELH
    clrf    ANSEL
    
    banksel TRISA
    
    clrf    TRISA
    clrf    TRISB
    clrf    TRISC

    banksel PORTA
    
    clrf    PORTA
    clrf    PORTB
    clrf    PORTC    
;____________________________________________________________________________________________________________________ 
       
Main: 
    call    Delay100        ;LCD settling time
    call    Initialise_LCD

	clrf	count			;set counter register to zero
	
Message		
    movf	count,w		    ;put counter value in W
    call	Text			;get a character from the text table
	xorlw	0x00			;is it a zero?
	btfsc	STATUS, Z
	goto	NextMessage
	call	LCD_Char
	call	Delay255
	incf	count, f
	goto	Message
	
;____________________________________________________________________________________________________________________

NextMessage	
    call	LCD_Line2		;move to 2nd row, first column
	
	clrf	count			;set counter register to zero
Message2
    movf	count, w		;put counter value in W
	call	Text2			;get a character from the text table
	xorlw	0x00			;is it a zero?
	btfsc	STATUS, Z
	goto	EndMessage
	call	LCD_Char
	call    Delay255
	incf	count, f
	goto	Message2

EndMessage	
		
Stop		
        goto	Stop			;endless loop  
;____________________________________________________________________________________________________________________ 
    
Initialise_LCD
    movlw   b'00111100'     ;8 bit mode / 2 lines / 5x11
    call    LCD_CMD
    movlw   b'00011100'    ;display shift / right shift. 
    call    LCD_CMD
    movlw   b'00000110'     ;Character entry mode
    call    LCD_CMD
    movlw   b'00001111'     ;display on / cursor off / cursor position on
    call    LCD_CMD
    call    LCD_Clr
    retlw   .0
;____________________________________________________________________________________________________________________ 
    
LCD_CMD
    movwf   PORTC
    bcf     LCD_RS
    call    Pulse_E
    call    Delay5
    retlw   .0    
;____________________________________________________________________________________________________________________    
    
LCD_Char
	movwf	LCD_PORT
	bsf	    LCD_RS	        ;RS line to 1
	call	Pulse_E			;Pulse the E line high
	call 	Delay5
	retlw	0x00
;____________________________________________________________________________________________________________________

LCD_Line2
    movlw	0xc0			;move to 2nd row, first column
	call	LCD_CMD
	retlw	0x00

LCD_Clr
    movlw	0x01			;Clear display
	call	LCD_CMD
	retlw	0x00   
;____________________________________________________________________________________________________________________ 
    
Delay255
    	movlw	0xff		;delay 255 mS
		goto	d0
Delay100
    	movlw	d'100'		;delay 100mS
		goto	d0
Delay50
		movlw	d'50'		;delay 50mS
		goto	d0
Delay20
    	movlw	d'20'		;delay 20mS
		goto	d0
Delay5
		movlw	0x05		;delay 5.000 ms (4 MHz clock)
d0		movwf	count1
d1		movlw	0xC7		;delay 1mS
		movwf	counta
		movlw	0x01
		movwf	countb
Delay_0
		decfsz	counta, f
		goto	$+2
		decfsz	countb, f
		goto	Delay_0

		decfsz	count1	,f
		goto	d1
		retlw	0x00   
;____________________________________________________________________________________________________________________ 
    
Pulse_E
        bsf     LCD_E
        nop
        bcf     LCD_E
        retlw   .0
;____________________________________________________________________________________________________________________  
            	
Text		
        addwf	PCL, f
		retlw	'A';'H'
		retlw	'B';'e'
		retlw	'C';'l'
		retlw	'D';'l'
		retlw	'E';'o'
		retlw   'F'
		retlw   'G'
		retlw   'H'
		retlw   'I'
		retlw   'J'
		retlw   'K'
		retlw   'L'
		retlw   'M'
		retlw   'N'
		retlw   'O'
		retlw   'P'
		retlw	0x00
		
Text2		
        ADDWF   PCL, f
        RETLW   'R'
        RETLW   'S';'e'
        RETLW   'T';'a'
        RETLW   'U';'d'
        RETLW   'V';'y'
        RETLW   'W';'.'
        RETLW   'X';'.'
        RETLW   'Y';'.'
        retlw   'Z'
        RETLW   0x00 
 end
 

Nigel Goodwin

Super Moderator
Most Helpful Member
You're just doing something wrong - a short on one of the pins perhaps?.

Easy to check what it is - write out the ASCII codes for 'Hello Ready' in binary, and then write out the binary codes for what you actually displayed.

This will easily allow you to spot with bit has the problem, it may be something stupid like you're feeding it from RA4 and don't have a pullup resistor - but a binary representation will quickly show you where the problem is.
 
Hi,

Ok, thanks Nigel. I had transposed B0 and B1 wires to the display :eek:. I'm such a doofus! When will I learn? - ALWAYS CHECK THE BASICS :)

Thanks again.
 
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