John Coppens wrote 2012-08-24 21:17:
> Hello all...
>
> As mentioned in my mail, I submitted the strange behaviour I
> experienced with mplab x to the Microchip bug list, and got as answer:
>
> <paraphrased>
> We believe that this is due to the read-modify-write
> nature of the bsf instructions. You should keep an image and update the
> image
> </paraphrased> (...and closed the bug)
>
> If I understand the RMW behaviour, then the possible problems are due
> to either capacitive (or other) loading of the outputs, or having some
> internal peripheral enabled which could cause the same loading.
>
> Is there any way this could explain my problem? I even tried the
> 'image' method to update port A, and the mplab X simulator _still_
> doesn't show any change to the port A output.
>

Now, Note that the RWM problem *never* hits the *same pin* as
your are BCF/BSF'ing !!

The RWM problem will show up as random changes of *other* pins
then the one you are targeting with your BCF/BSF. Usualy another
pin changed with a BCF/BSF directly before the other BCF/BSF.
That is when the RMW might reset the first pin since it hadn't
had time to get to a stable level on the pin.

Now, it you are BSF'ing a pin that is configured as an
analog input, it *should* show as "0" in the simulator
because that is how the hardware sees it. But *that*
is *not* a RWM issue ! It's absolutely normal. :-)


Have you given them a reproducer?
That is, actual code that shows the problem?


Jan-Erik.


> Am I really that far off my game? Could someone try to run this code and =
check
> if they have the same problems? (MPLAB X is Linux 64bit version 1.30 here=
)
> Gpsim and the actual hardware say I'm right...
>
> John
>
> BSF Code:
>                  processor pic16f874
>                  include   P16F874.INC
>
>                  org     0
>
>                  goto    start
>
> 		org     4
>
> start
> 		banksel TRISA
> 		movlw   b'00000111'
> 		movwf   ADCON1
>
> 		movlw   b'00111001'
> 		movwf   TRISA
>
> 		clrf    TRISB
>
> 		banksel PORTA
> loop
> 		bsf     PORTA,1
> 		bsf     PORTA,2
>
> 		bcf     PORTA,1
> 		bcf     PORTA,2
>                  goto    loop
>
>                  end
>
> Direct modification code (no RMW): ---------------------------
>
>                  processor	pic16f874
>                  include 	P16F874.INC
>
>                  org             0
>
>                  goto    start
>
>                  org             4
>
> start
> 		banksel TRISA
> 		movlw   b'00000111'
>                  movwf   ADCON1
>
> 		movlw   b'00111001'	; Bits 1 & 2 as outputs
> 		movwf   TRISA
>
> 		clrf    TRISB
>
> 		banksel PORTA
> loop
> 		movlw   2
> 		movwf   PORTA
> 		movlw   6
> 		movwf   PORTA
> 		movlw   4
> 		movwf   PORTA
> 		movlw   0
> 		movwf   PORTA
>
> 		goto    loop
>
> 		end
>
--=20
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