Hi,

Thanks for all the tips guys, they were very helpful, and i've made the
changes to my code. However, when running the dry run/debug feature of MPLAB
the PORTA value never changes, even after changing it to what you have
recommended.  Here is the new code, coudl you please enlighten me on what
I'm doing wrong.

Thanks

P.S I programmed the chip, and it doesn't flash the LED's as the debugger
said.

Code---------------------


;Setup
 list P=16F877
 include "c:\P16F877.inc"
 errorlevel -302
 __CONFIG _CP_OFF & _XT_OSC & _WDT_OFF & _PWRTE_OFF & _BODEN_OFF & _LVP_OFF
;Declarations
d1 equ 20h
d2 equ 21h
d3 equ 22h
 org 0
 call  Start

Bank1 Macro
 bsf STATUS,RP0
 bcf STATUS,RP1
 bcf STATUS,IRP
 Endm

Bank0 Macro
 bcf STATUS,RP0
 bcf STATUS,RP1
 bcf STATUS,IRP
 Endm

Init Bank1
 movlw b'11110000' ;0,1,2,3 of porta are output
 movwf TRISA
 Bank0 ;bank 0
 movlw b'00001010' ;all porta low
 movwf PORTA
 retlw 0


Delay
   ;4999993 cycles
 movlw 0x2C
 movwf d1
 movlw 0xE7
 movwf d2
 movlw 0x0B
 movwf d3
Delay_0
 decfsz d1, f
 goto $+2
 decfsz d2, f
 goto $+2
 decfsz d3, f
 goto Delay_0

   ;3 cycles
 goto $+1
 nop

   ;4 cycles (including call)
 return

Start call Init
Main movlw b'00000001'
 movwf PORTA
 call Delay
 movlw b'00000010'
 movwf PORTA
 call Delay
 movlw b'00000100'
 movwf PORTA
 call Delay
 movlw b'00001000'
 movwf PORTA
 call Delay
 goto Main
 End


----- Original Message -----
From: "Jinx" <joecolquitt@CLEAR.NET.NZ>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, November 29, 2002 5:19 PM
Subject: Re: [PIC]: First ASM problems


> > a book i've read says to declare, then initialize, then other
subroutines,
> > then start, then main functions.
>
> Some people do write that way. Personally I prefer my main code at
> the start and routines after. I have trouble wading through subroutines
> to get to what's calling them. Tidy code is a lot easier to debug
>
> So, with that bias, my layout preferences and Dr Bartfai's comments
> in mind -
>
> ( = indicates a space, I don't use tabs)
>
> ====list P=16F877
> ====include "c:\P16F877.inc
>
> ;----------------------------
> ;You can suppress error messages
> ;
> =errorlevel -305, -302, -306
>
> ;----------------------------
> ;You need to set CONFIG, eg (all on one line)
>
> =__CONFIG _CP_OFF & _XT_OSC & _WDT_OFF & _PWRTE_OFF & _BODEN_OFF &
_LVP_OFF
>
> ;Declarations
>
> d1====equ===20
> d2====equ===21
> d3====equ===22
>
> ;------------------------------
> ;You can also define variables in a block of memory
>
> ====cblock 0x20==========;this declares variable RAM address
>
> ====d1
> ====d2
> ====d3
>
> ====endc
>
> ;specifically define port pins eg
>
> #define===led1====porta,0
> #define===led2====porta,1
> #define===led3====porta,2
> #define===led4====porta,3
>
> ;eg   bsf    led1
>
> ;and make macros for bank selection (there is another way - Olin ?)
>
> bank0=macro
> =========bcf====status,rp0
> =========bcf====status,rp1
> =========bcf====status,irp
> =========endm
>
> bank1=macro
> =========bsf====status,rp0
> =========bcf====status,rp1
> =========bcf====status,irp
> =========endm
> ;------------------------------
>
> ====org=0x000
> ====goto=init
>
> ;-----------------------------
> ;If you're using interrupts
>
> ====org=0x004
> ====goto=isr
> ;----------------------------
>
> Init=====movlw==b'00000000'======;all porta low
> =======movwf==PORTA
>
> =======bsf====STATUS,RP0=====;bank 1
> =======bcf====STATUS,RP1
>
> ;or use the macro to change bank. Simply type
>
> =======bank1
>
> =======movlw==b'11110000'======;0,1,2,3 of porta are output
> =======movwf==TRISA
>
> =======bcf==== STATUS,RP0=====;bank 0
>
> ;or
>
> =======bank0
>
> Main===bcf=====PORTA,1========;be aware of read-modify-write
> =======nop====================;problems that may occur when
> =======bcf=====PORTA,2========;changing port pin data
> =======nop
> =======bcf=====PORTA,3
> =======nop
> =======bsf=====PORTA,0
> =======call=====Delay
> <snip>
> =======goto====main
>
> Delay===movlw 0x2C===========;4999993 cycles
> <snip>
> =======return
>
> =end
>
> =======================================================
>
> > I get  a stack underflow error
>
> Because you had org 0x000 set to INIT, not START. The first piece of
> code encountered ended with a RETLW that had no CALL
>
> --
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