See comments on your code below:-

>
> test    EQU     01AH
>
>      ORG 0                       ; Reset vector at 0
>    LIST

That "LIST" shouldn't be in there.

>   __CONFIG _CONFIG1H, _OSCS_OFF_1H & _HS_OSC_1H
>   __CONFIG _CONFIG2L, _BOR_ON_2L & _PWRT_ON_2L & _BORV_45_2L
>   __CONFIG _CONFIG2H, _WDT_OFF_2H  & _WDTPS_1_2H
>   __CONFIG _CONFIG3H, _CCP2MX_ON_3H
>   __CONFIG _CONFIG4L, _STVR_OFF_4L & _LVP_OFF_4L & _DEBUG_OFF_4L
>   __CONFIG _CONFIG5L, _CP0_OFF_5L & _CP1_OFF_5L & _CP2_OFF_5L
> & _CP3_OFF_5L
>   __CONFIG _CONFIG5H, _CPB_OFF_5H & _CPD_OFF_5H
>   __CONFIG _CONFIG6L, _WRT0_OFF_6L & _WRT1_OFF_6L &
> _WRT2_OFF_6L & _WRT3_OFF_6L
>   __CONFIG _CONFIG6H, _WRTC_OFF_6H & _WRTB_OFF_6H & _WRTD_OFF_6H
>   __CONFIG _CONFIG7L, _EBTR0_OFF_7L & _EBTR1_OFF_7L &
> _EBTR2_OFF_7L & _EBTR3_OFF_7L
>   __CONFIG _CONFIG7H, _EBTRB_OFF_7H
>
>

I'd recommend you put the config stuff in another ASM file in your project.
makes things neater.

> ;
> ; Pseudo-code: (there is a LED connected to bit 1 of PORTC)
> ; The LED should never light, as bit0 is always zero.
> ;
> ;     Set PORTC to output
> ;     Clear PORTC
> ;     Clear TEST
> ;Loop:if bit0 of TEST is 1 then
> ;         toggle bit1 of portc             'toggle the LED
> ;     endif
> ;     goto loop
>
>
>          clrf    TRISC           ; Set portc to output
>          clrf    portc           ; Set portc pins low (LED is OFF)
>
>          CLRF    test            ; Clear the variable

Above you specified "org 0x00". So, these first three instructions go to
program memory addresses 0x0000, 0x0002 and 0x0004.

> ;
> ; Problem seems to occur when the target of the goto is an
> ; address that is NOT a multiple of 4.
> ; In the code below, L1 is at 14H. By changing the ORG
> statement ; or removing the NOP in the loop, or by adding
> another NOP - doing anything ; such that L1 ends up at an
> address that is a multiple of 4, the code works. ; That is,
> the LED does not flash. ; ; Also, by adding code (NOPs will
> do) AFTER the statement at L1, the code works
>
>
>         ORG 000aH

oops, you just gave another ORG. so, the program memory from 0x0006 up to
0x0009 is uninitialised. But you didn't branch over it. Who knows what it
contains?


> LOOP    BTFSS   test,0          ; IF bit0 is 1, skip to toggle LED
>          GOTO    L1              ; Bit0 is 0, don't toggle
>
> ; NOTE: we should never get here, since "test" was cleared
> initially ; but we do! ; The LED flashes at an irregular
> rate, as if sometime ; "test" is zero and sometimes not. ;
> Other tests have shown that "test" IS ALWAYS ZERO
>
>          BTG     PORTC,1       ; Toggle the LED
> ; If this NOP is removed (or if another one is added), the
> code works as it should
>          nop
> L1      BRA     LOOP
>

I prefer to put labels on separate lines:-
L1:
                BRA     LOOP


Anyway, the fact that you're trying to execute un-programmed program memory
might be the cause of the problem here. I guess it depends on what your
programmer does with this memory.

Just lose the second ORG (the ORG 000aH).

Jon

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