Hi Dennis,

As I understand it, this is a feature of all PICs - Not just the 16C5x
(Definitly on the 16C84).  And, you should be aware that if you read a pin
that is pulled high (or low) when you have programmed it into the
complementary state, you'll find that afterward, it will be set to this value.

For the read, when you look at the block diagrams in the data sheets, you'll
see that the input buffers are connected directly to the bi-directional
internal data bus.  I've never heard an explanation why the read causes the
output buffers to change state, but I suspect that it's because the output
latches are on the bi-di bus and there is a universal "write" clock signal
at the end of each instruction (when this happens the PORT select is active
and the data from the input buffers is on the internal data bus).

This can be a problem if you are have a read and a write device on the same
pin.  You cannot save your output state in the Port and hope to have it
still valid after you read the input device.  This means that when you are
changing from Read to Write, you must write your expected state before
changing the TRIS bits.

I hope I've explained this a) clearly and b) accurately.  If I've made any
mistakes, please jump in.

Myke

It will most likely rear it's ugly Yes, this is present for
>Hi there.
>
>While reading the PIC 16/17 Databook I noticed the following
>about the 16C54.
>
>"A read of the ports reads the pins, not the output data latches,
> i.e., if an output driver on a pin is enabled and driven high,
> but the external system is holding it low, a read of the port
> will indicate that the pin is low."
>
>This isn't mentioned in the datasheet about the 16C84.
>Now my question is, does the 16C84 support this too?
>
>Any help is appreciated.
>
>Dennis.
>******************************************************************************
>*             -=[ Dennis Velthuis =-    -= denv@htsa.hva.nl ]=-              *
>*                 -=[ Raving His Way Into Tha Future :-) ]=-                 *
>*                  -=[ http://htsa.htsa.hva.nl/~denv ]=-                     *
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>

Do you ever feel like an XT Clone caught in the Pentium Pro Zone?