I must be doing something wrong here, but the problem eludes me...

Using 16F872, Port A is setup as all outputs, and all digital, but
when I write 0xFF to Port A, RA<4> does not come go high.  I've
tested the LED, the resistor, and even the breadboard connection
by jumpering a wire from the IC pin to the LED.

RA4 also serves as T0CKI (external clock), but I have that setup
for internal clock, and am successfully using TMR0 to generate
a clock pulse, so that confirms to me that it's not configuring that
pin as an external clock input.

Here are snippets of the code, and there are no other references
to PORTA anywhere in the code.  See the line marked "XXX" in the
comment field -- this was added to test PORTA configuration when
I first saw the odd results.


        LIST P=16F872
        INCLUDE "p16f872.inc"
        ERRORLEVEL -224
        __CONFIG _PWRTE_ON & _LP_OSC & _WDT_OFF & _LVP_OFF

        CBLOCK  H'20'

<code snipped>

        ORG     0x00
        goto    Init

        ORG     0x04
        goto    ISR


;-------------------------------------------------------------------
;   Initialization section
;-------------------------------------------------------------------

Init:
        bsf     STATUS,RP0      ; Select bank 1
        bcf     STATUS,RP1      ; ...

        movlw   B'00000110'
        movwf   ADCON1          ; Port A is all digital
        movlw   B'00000000'
        movwf   TRISA           ; Port A is all outputs
        movlw   B'11100000'
        movwf   TRISB           ; RB7:5 are inputs, RB4:0 outputs
        movlw   B'00000000'
        movwf   TRISC           ; Port C is all outputs

        movlw   B'00000100'     ; Port B pullups enabled, internal ...
        movwf   OPTION_REG      ; ... clock, prescaler 1:32

<code snipped>

;---------------------------------------------------------------------
;   Main code routine
;---------------------------------------------------------------------

Main:
        ;----- Ensure that we're in bank 0 -----
        bcf     STATUS,RP0      ; Select bank 0
        bcf     STATUS,RP1      ; ...


        ;----- Primary loop -----
MainLoop:

<code snipped>

;***** TEMP DEBUG ***** Show value of button states on PORT A
        clrf    TMPREG2
        btfsc   BTN_MODE,7
        bsf     TMPREG2,0
        btfsc   BTN_MODE,6
        bsf     TMPREG2,1
        btfsc   BTN_UP,7
        bsf     TMPREG2,2
        btfsc   BTN_UP,6
        bsf     TMPREG2,3
        btfsc   BTN_DOWN,7
        bsf     TMPREG2,4
        btfsc   BTN_DOWN,6
        bsf     TMPREG2,5
        movf    TMPREG2,W
        movlw   H'FF'           ; XXX Override and light up all PORT-A LED's.
        movwf   PORTA
;*****

        goto    MainLoop

<code snipped>



For grins, I tried another 16F872, but got the same odd
results, so it's not the chip.
Thanks for any thoughts...

Cheers,
-Neil.

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