>> MOVF PORTB,W
>> MOVWF SHADOWB
>> MOVLW B'100'
>> IORWF SHADOWB,W
>> MOVWF PORTB
>>
> 
> One thing to watch out for here is interrupts. If you write to another pin in 
> port B in the interrupt routine, a bit banged serial output for example, you 
> have to make sure that the interrupt routine isn't executed between when you 
> read the content of the port to the shadow register until you write it back. 
> Otherwise the change made by the interrupt routine will be undone when you 
> write back the shadow register.

Good programming practice would dictate that the interrupt routine also 
uses the shadow, so there would be no problem.

-- 

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu

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