Just a suggestion. 
Make sure that the data is presented and the RS line set to its correct
state and then toggle the E line. I don't like the E line high when
presenting the data I think it has the potential for trouble... Ohh and a
gotcha... RAA4 is open drain have you fitted the resistor ???

Steve

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
threewheeler7
Sent: 07 January 2010 20:12
To: piclist@mit.edu
Subject: [PIC] 24x1 LCD Hello World Prog Blank Screen. (ASM)


I am using the now famous WDC2401P 24x1 LCD from AllElectronics. For those
of
you that do not know this LCD, it is famous because it runs $.99-$1.85,
making it one of the cheapest alpha-numeric LCDs on the internet. It is
cheep because, 1. It is hardwired for 8-bit mode, 2. It's connector has its
pins spaced at a non-standard .05" spacing, and 3. It's controller is an
HD66717, not the more common Hitachi 44780 controller.
    I have many programs I would like to port over to this cheep LCD, but
when writing a simple test program for it, I get nothing on the screen. My
code is based on the HD66717's data sheet, the LCD's data sheet, and the
useful info on this particular LCD at
http://www.serialwombat.com/parts/lcd111.htm, which I thought explains the
protocol pretty clearly. I have gone over it and over it and I cannot seem
to see anything wrong with my code, or circuit, I need another set of eyes.

I have it hooked up as follows:  LCD's E line to RA2, LCD's RS line to RA4,
LCD,s Reset line to RA3, and LCD D0-D7 to RB0-RB7. LCD's R/W pin is tied to
ground.


Code:

	LIST	p=16F648a		;tell assembler what chip we are
using
	#include "P16F648a.inc"		;include the defaults for the chip
	__config 0x3D18	;Internal osc IO on RA6/RA7, WDT off, PUT off, MCLRE
disabled, BODEN disabled, LVP disabled, CPD disabled, CP off
	


#DEFINE	LCD_E	PORTA,2
#DEFINE LCD_RS	PORTA,4
#DEFINE	LCD_RESET	PORTA,3

	cblock 0x20
	LCD_Temp
	count1
	counta
	countb
	countc
	endc




			   org    0x00

Setup
	movlw	0x07
	movwf	CMCON	;turn comparitors off

   	bsf 	STATUS,		RP0	;select bank 1
   	movlw 	b'00100000'	;all but RA5 output	
   	movwf 	TRISA
	movlw 	b'00000000'	;all output
   	movwf 	TRISB
	bcf	STATUS,		RP0	;select bank 0
	clrf	PORTB
	clrf	PORTA
	bsf		LCD_RESET
	call	Delay255
	call	LCD_Init
	

Start
	movlw	'H'				;Print "Hello World!"
	call	LCD_Char
	movlw	'e'
	call	LCD_Char
	movlw	'l'
	call	LCD_Char
	movlw	'l'
	call	LCD_Char
	movlw	'o'
	call	LCD_Char
	movlw	' '
	call	LCD_Char
	movlw	'W'
	call	LCD_Char
	movlw	'o'
	call	LCD_Char
	movlw	'r'
	call	LCD_Char
	movlw	'l'
	call	LCD_Char
	movlw	'd'
	call	LCD_Char
	movlw	'!'
	call	LCD_Char
Stop
	goto	Stop		; Endless loop


LCD_Init
	bcf		LCD_RESET	;bring reset pin low for 20Ms to
reset controller
	call	Delay20
	bsf		LCD_RESET	;bring back high
	call	Delay20
	movlw	0x1c	;Turn on the lcd driver power
	call	LCD_Cmd
	movlw	0x14	;Turn on the character display
	call	LCD_Cmd	
	movlw	0x28	;Set two display lines (The hd66717 considers 12
characters to
be a line. Our 24 character display is actually two 12-character lines right
next to each other).
	call	LCD_Cmd
	movlw	0x4f	;Set to darkest contrast
	call	LCD_Cmd
	movlw	0xe0	;Set the data address to the first character
	call	LCD_Cmd
	return
LCD_Clr
	movlw	0x01	;clear LCD 
	call	LCD_Cmd
	return

LCD_Char
	bcf		LCD_E		;Make sure Enable line is low
	nop
	bsf		LCD_RS		;Bring register select HIGH to go to
data reg
	nop
	bsf		LCD_E		;Bring Enable line high
	nop
	movwf	PORTB		;Present data to port
	nop
	bcf		LCD_E		;Bring data line back low
	call	Delay5		;Delay 5 Ms between data and commands  
	return

LCD_Cmd
	bcf		LCD_E		;Make sure Enable line is low
	nop
	bcf		LCD_RS		;Bring register select LOW to go to
command reg
	nop
	bsf		LCD_E		;Bring Enable line high
	nop
	movwf	PORTB		;Present data to port
	nop
	bcf		LCD_E		;Bring data line back low
	call	Delay5		;Delay 5 Ms between data and commands  
	return


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 5ms 
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
	end
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