I am quite sure Olin is incorrect here. The statement "TEMP = PORTB" would
almost certainly become "MOVF PORTB,W" and "MOVWF TEMP". The "MOVF"
instruction will not affect the PORTB latch because it is NOT
read-modify-write (although MOVF PORTB,F would be).

Bob Ammerman
RAm Systems

----- Original Message -----
From: "Olin Lathrop" <olin_piclist@EMBEDINC.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, May 22, 2002 7:48 AM
Subject: Re: [PIC]: State of output drivers after a tris change


> > > TRISB = 0
> > > PORTB = 0xAA
> > >
> > > TRISB = 255
> > > TEMP = PORTB
> > >
> > > TRISB = 0
> > >
> > > After to port is set back to output what will be the state of the
pins?
> > > Does the contents of the output driver get destroyed when changing
TRIS,
> or when performing a read operation on the port? I'm hoping that my
original
> value ( AA ) is presented on the pins when I switch back to output mode.
> >
> > It should still be 0xAA because you did nothing to change the PORTB
> > output value.
>
> Actually he did, so it won't be.  TEMP = PORTB (assuming I interpret his
> pseudo code correctly) reads port B while all bits are set as inputs.
This
> will essentially copy the input values to the output latches.  The
resulting
> port B value therefore depends on the external circuit.
>
>
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