> >> 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 whe=
n 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.
> =


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 when t=
he =

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

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

/Ruben
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D

-- =

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