Jim,

 I see you are using the INTRCOSC, and I assume it defaults to 4mhz
since I don't see any frequency setting code.  So, if that is the case,
the only thing I can see that might be an issue is that you are
switching
PORTB on and off at about a 1 MHZ rate, so if you have LED's connected,
all you'll probably see is a Dim LED brightness.  Look at the pins with
a scope to see if they are actually toggling.  Or add a delay after you
tunr PORTB on, and again after you turn it OFF so you have time to see
if they are toggling.

Regards,

Jim

> -------- Original Message --------
> Subject: PIC16F876A not changing output pins
> From: Jim <picster733@gmail.com>
> Date: Thu, March 03, 2011 10:05 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.  Here is my assembly code:
>=20
> list      p=3D16f876a            ; list directive to define processor
> #include "p16f876a.inc"        ; processor specific variable definitions
>  __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.
> ; The lables following the directive are located in the respective .inc
> file.
> ; See respective data sheet for additional information on configuration
> word.
>=20
> ;***** VARIABLE DEFINITIONS
> ;; w_temp        EQU     0x70        ; variable used for context saving
> ;; status_temp   EQU     0x71        ; variable used for context saving
>=20
> ;**********************************************************************
> ORG     0x000             ; processor reset vector
> clrf    PCLATH            ; ensure page bits are cleared
> ;   goto    main  ;
>=20
>=20
> ;; initialize PORTA
> bcf STATUS, RP0 ; select bank 0
> bcf STATUS, RP1
> clrf PORTB
>=20
> bsf STATUS, RP0 ; select bank 1
> movlw 0x06
> movwf ADCON1
> movlw 0x00
> movwf TRISB
>=20
> top:
> bcf STATUS, RP0 ; select bank 0
> movlw 0x00
> movwf PORTB
> movlw 0xFF
> movwf PORTB
> goto top
> END                       ; directive 'end of program'
>=20
> Is there something wrong with this code, or is it definitely a hardware
> issue?
>=20
> Thanks,
> Jim
> --=20
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