Wouter van Ooijen escreveu:
> Ruben J=F6nsson wrote:
>   =

>>>>> MOVF PORTB,W
>>>>> MOVWF SHADOWB
>>>>> MOVLW B'100'
>>>>> IORWF SHADOWB,W
>>>>> MOVWF PORTB
>>>>>           =

>
>   =

>> Yes, there still could be problems if the interrupt is just after IORWF =

>> SHADOWB,W. Then changes done in the interrupt routine will be undone whe=
n the =

>> non interrupt code does MOVWF PORTB. The key is, appart from using a sha=
dow =

>> register, is to never read back from the port to the shadow register.
>>     =

>
> Hmmm you are right. But I don't understand your solution?
>
>     BSF shadow, 0
>     MOVFW shadow
>     =3D=3D=3D> interrupt here
>     MOWF port
>
> This sequence does not read the port, but changes made by the interrupt =

> would still be lost.
>   =

All you need is to disable the interrupts before and re-enable after the
sequence.
Sometimes you don't have a choice.

For absolutely most uses, this very short period (4 TCy including
disabling and re-enabling time) with interrupts off will not degrade the
performance:

bsf shadow,0
bcf INTCON,GIE
movfw shadow
movwf PORTx
bsf INTCON,GIE

The interrupt latency will increase at most by 3 TCy.

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