At 01:28 PM 4/30/01 -0500, Mike Mansheim wrote:
>I think I've just run into a rwm effect, but not because I'm changing
>port directions.
>F876 portA configured as follows (set once, doesn't change):
>RA0, RA3:       analog in
>RA1, RA2, RA5:  out
>RA4:            digital in
>ADCON1:  RA0,1,3 as analog in, RA2,5 as digital i/o.
>Whenever RA2 or RA5 are changed, RA1 goes low unexpectedly.
>My questions are:
>- have I diagnosed the problem correctly?
>- I can fix this by simply refreshing RA1 to it's correct state after
>   any operation on the rest of the port.  Is this ok, or is there some
>   bigger problem with using an analog input pin as a digital output?

Yes to both.  Hopefully, whatever is being fed by pin RA1 won't get upset
by the glitch.

You can avoid the problem by not using R-M-W operations on that port.  Use
a separate register (often called a "shadow register") for your bit
manipulations.  Then write that register to the port.

dwayne



Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 17 years of Engineering Innovation (1984 - 2001)

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