At 11:53 AM 5/8/98 +0200, you wrote:
>
>Not true, the problem you have noticed is also if the port pin are all
>outputs and you don't change direction. You are correct to say that
>write to port is actually read/modify/write but the read part gets the
>value _directly_ form the output pins. So if your program drives bit 3
>high but the corresponding pin is tied to ground the read operation gets
>a '0' for that bit. When the PIC writes back the modifyed value to the
>port the bit 3 is written as '0'.

I have often heard this mentioned as a caveat about the PIC, but why should
one expect the PIC to even work at all with one of its pins shorted to low?
Under this condition, the PIC would probably be outputting full IO pin
current, maybe over-spec. I don't see why one wouldn't just check their
hardware for shorts and other mistakes, instead of using this register
shadowing technique in a final design.


Sean


+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
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