problem with PIC16F877+LCD display

[meera83]

i m asking to use PIC16F877 to do a text display on LCD..
the LCD that i use is on the PICDEM 2PLUS...

i had wrote the code to display the text, but it seen like show nothing..
i don't know where my mistake is....

 

[Pommie]

You appear to have initialisation code for 8 bit mode and write data for 4 bit mode. Have you combined code from 2 different sources?

As a starting point, look at Nigel's LCD tutorial. He should be around soon and the link is in his sig + in the sticky.

Mike.

 

[meera83]

combined code from 2 different sources??

i don't understand with what you mean..is it my source code have mistake? may i know which part of code should i correct it??
i only program this file inside PIC, no any other file...

yap, before that, i had go through Nigel's LCD tutorial 3..
since i had to use PICDEM 2 PLUS to program it and display on its LCD, i had to change the code inside the tutorial(for the port pin)..

since i new to LCD step source code, i fail to make the LCD work...the LCD display seen like didn't have any respond...

thanks..May You Be Well And Happy...

 

[Pommie]

You appear to have bit 7 of the LCD connected to Port D bit 3.
You then write a full byte in INIT_LCD.

INIT_LCD
	BCF		PORTA,3
	MOVLW	b'00101000'			;10h + 08h
	MOVWF	PORTD

You then write 4 bit data in

LCD_Char	movwf		templcd
		swapf		templcd,w		;send upper nibble
		andlw		0x0f			;clear upper 4 bits of W
		movwf		PORTD
		bsf		PORTA,3			;RS line to 1
		call		Pulse_e			;Pulse the E line high

		movf		templcd,w		;send lower nibble
		andlw		0x0f			;clear upper 4 bits of W
		movwf		PORTD

This last bit of code looks like Nigel's.

This is why I can't follow your code. It switches from 8 bit to 4 bit. It cannot be both.

I would suggest modifying Nigel's code and get that working first.

Mike

 

[meera83]

i just edit the source code from example using 8-bit data bus LCD...

since the LCD that i used on PICDEM 2 PLUS which the connection is for 4-bit data bus LCD, so i copy the 4-bit source code from Nigel's example..

i didn't understand with the step of code should go through, so i unable to write a right code..

ok, i will try to understand with the Nigel's tutorial 3 and do some editing from the code..

that Nigel's code is it just need to load with one file?don't need load other file?

thanks...

 

[Nigel Goodwin]

that Nigel's code is it just need to load with one file?don't need load other file?

Each of my tutorials is fully working as it is, just the one file.

 

[House0Fwax]

	movlw		b'110001'
	movwf		TRISA

I may well be wrong here, but that doesn't look right to me.

 

[Nigel Goodwin]

	movlw		b'110001'
	movwf		TRISA

I may well be wrong here, but that doesn't look right to me.

I would be much happier with 8 bits in the binary value - I'm always concerned that I'm not 100% sure which way the assembler might justify the 6 to 8!.

 

[Pommie]

I would be much happier with 8 bits in the binary value - I'm always concerned that I'm not 100% sure which way the assembler might justify the 6 to 8!.

It would of course take B'1' as 128.

Mike

 

[Pommie]

P.S. I quoted the wrong post. The irony is fully appreciated.

 

[meera83]

I would be much happier with 8 bits in the binary value - I'm always concerned that I'm not 100% sure which way the assembler might justify the 6 to 8!.

movlw b'110001'
movwf TRISA

the PIC16F877 got only 6 bits RA0-RA5, so i just b'110001' not b'8 bit'...

thanks..

 

[Nigel Goodwin]

movlw b'110001'
movwf TRISA

the PIC16F877 got only 6 bits RA0-RA5, so i just b'110001' not b'8 bit'...

thanks..

But W has 8 bits, so are you loading it's top 6 bits?, or it's bottom 6 bits? - like I said, I'd be MUCH happier to see 8 bits so you KNOW it's correct.

You can't load W with only 6 bits, so make sure it's loading the bits in the place you want.

 

[eng1]

Obviously he would be on the safe side using 8 bits (I do that every time), but actually he's loading the six less significant bits of the TRISA register.

 

[Nigel Goodwin]

Obviously he would be on the safe side using 8 bits (I do that every time), but actually he's loading the six less significant bits of the TRISA register.

Probably so - but I would have to look it up (probably every time I used), and then I'd disassemble the HEX file to make absolutely sure!

Far easier to do it with 8 bits in the first place!.

 

[Pommie]

I assumed everyone was talking tongue in cheek and joking around.
If you see movlw 0x9 (only 4 bits) do you assume it will add a trailing zero and load 0x90 into W.
When I posted above, "It would of course take B'1' as 128." I was joking.
I don't think I have ever come across a situation where you add trailing zeroes.

Mike.

 

[Nigel Goodwin]

I assumed everyone was talking tongue in cheek and joking around.
If you see movlw 0x9 (only 4 bits) do you assume it will add a trailing zero and load 0x90 into W.
When I posted above, "It would of course take B'1' as 128." I was joking.
I don't think I have ever come across a situation where you add trailing zeroes.

I'm VERY distrustful

 

[meera83]

Help!Help! i really don't know what can i do with the source code..

I had make some changing to Nigel's LCD tutorial according to my port pin,
from PICDEM 2 PLUS circuit shcematic, the port pin
RA1 - E
RA2 - RW
RA3 - RS

DB4 - RD0
DB5 - RD1
DB6 - RD2
DB7 - RD3

but the LCD still don't have any respond..

 

[meera83]

Help!Help! i really don't know what can i do with the source code..

I had make some changing to Nigel's LCD tutorial according to my port pin,
from PICDEM 2 PLUS circuit shcematic, the port pin
RA1 - E
RA2 - RW
RA3 - RS

DB4 - RD0
DB5 - RD1
DB6 - RD2
DB7 - RD3

but the LCD still don't have any respond..

this is the changing code that i program in PIC..

 

[meera83]

what's mean by this code?

LCD_RS Equ 0x04 ;LCD handshake lines
LCD_RW Equ 0x06
LCD_E Equ 0x07

if my port pin connection is like
RA1 - E
RA2 - RW
RA3 - RS

DB4 - RD0
DB5 - RD1
DB6 - RD2
DB7 - RD3

then what location should i write??

thanks..

 

[bananasiong]

this is the changing code that i program in PIC..

Your attachment is only this:

	list      p=16f877            ; list directive to define processor
	#include <p16f877.inc>        ; processor specific variable definitions
	
	__CONFIG _CP_OFF & _WDT_OFF & _BODEN_OFF & _PWRTE_ON & _LP_OSC & _WRT_ENABLE_OFF & _LVP_OFF & _DEBUG_OFF & _CPD_OFF 

; '__CONFIG' directive is used to embed configuration data within .asm file.
; The labels following the directive are located in the respective .inc file.
; See respective data sheet for additional information on configur