Jim,

 You should still add delays in the routine where you are changing the
state of PORTB.  A NOP between them should be enough to see if RMW is a
problem.

Regards,

Jim

> -------- Original Message --------
> Subject: [PIC] PIC16F876A not changing output pins
> From: Jim <picster733@gmail.com>
> Date: Thu, March 03, 2011 10:15 am
> To: piclist <piclist@mit.edu>
>=20
>=20
> Hello, I am having trouble with a PIC16F876A, on an Olimex 28-pin dev boa=
rd
> (see http://www.sparkfun.com/products/18).  The program downloads and
> verifies successfully (or so the software tells me) via an meLabs U2 USB
> programmer.  In the past, I've had a couple PIC18 chips partially die on =
me
> without losing their ability to be programmed, so I'm wondering if that's
> the case here, or if there's something wrong with my code.  I have been
> careful about grounding myself while handling both chips, although it's
> possible that I forgot at some point while working on it with little slee=
p.
>=20
>=20
> >
> I am trying to toggle all the pins of PORTB as a "hello world" test.  It
> works in the simulator, but apparently does nothing on the board.  I have
> already checked the supply voltage (+5.05V) and tested both chips on a
> breadboard with all the I/O ports connected to GND with 1k resistors as
> suggested here http://www.piclist.com/techref/logic/xtrapins.htm.  Still
> nothing on my scope, which is an old HP DSO with a 10 MHz sample rate.  H=
ere
> is my assembly code:
>=20
> >
> list      p=3D16f876a            ; list directive to define processor
>=20
> > #include "p16f876a.inc"        ; processor specific variable definition=
s
>=20
> >
> __CONFIG _CP_OFF & _WDT_OFF & _BODEN_ON & _PWRTE_ON & _RC_OSC & _LVP_OFF =
&
> _DEBUG_OFF & _CPD_OFF
>=20
> >
> ; '__CONFIG' directive is used to embed configuration data within .asm fi=
le.
>=20
> > ; The lables following the directive are located in the respective .inc
> file.
>=20
> > ; See respective data sheet for additional information on configuration
> word.
>=20
> >
> ;***** VARIABLE DEFINITIONS
>=20
> > ;; w_temp        EQU     0x70        ; variable used for context saving
>=20
> > ;; status_temp   EQU     0x71        ; variable used for context saving
>=20
> >
> ;**********************************************************************
>=20
> > ORG     0x000             ; processor reset vector
>=20
> > clrf    PCLATH            ; ensure page bits are cleared
>=20
> > ;   goto    main  ;
>=20
> >
>=20
> ;; initialize PORTA
>=20
> > bcf STATUS, RP0 ; select bank 0
>=20
> > bcf STATUS, RP1
>=20
> > clrf PORTB
>=20
> >
> bsf STATUS, RP0 ; select bank 1
>=20
> > movlw 0x06
>=20
> > movwf ADCON1
>=20
> > movlw 0x00
>=20
> > movwf TRISB
>=20
> >
> top:
>=20
> > bcf STATUS, RP0 ; select bank 0
>=20
> > movlw 0x00
>=20
> > movwf PORTB
>=20
> > movlw 0xFF
>=20
> > movwf PORTB
>=20
> > goto top
>=20
> > END                       ; directive 'end of program'
>=20
> >
> Is there something wrong with this code, or is it definitely a hardware
> issue?
>=20
> >
> Thanks,
> Jim
> --=20
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist


--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.