>
> Hi,
>
> I've been an observer of the PICLIST for some time and am impressed with
>some of the valuable responses given to questions asked. Forgive me if this
>question has been answered before, but I have a project in mind using a
>16F84. I am intersted in using a 93LC56 Serial EEPROM but am running out of
>pins. There are other ways of freeing an extra pin, but for simplicity, I
>was hoping that I could connect the Data In pin to the Data Out pin.
>
> The data sheet indicates it can be done, but that there is the possibility
>of a 'bus conflict'. This is where I got a bit lost. Has anyone used this
>approach and, if so, what do I need to watch out for?

A bus conflict occurs when the pin from the PIC driving Data In and the
Data Out from the EEPROM are both active at the same time. It's even worse
when one is set to high and the other to low because it causes a short which
of course is very very bad for the circuit.

The solution is simple. Put a current limiting resistor on Data Out so that
it cannot drive the bus at full current. Conflict resolved.

I believe the last time I did this I used either a 1K or a 2.2K resistor
between Data Out and the PIC. Worked like a champ.

BTW this bus conflict is always a transient event because Data Out is
usually tri-stated when not in use. So it's not like the PIC will have to
suck down current all the time. The conflict only exist long enough for
the PIC to finish sending the command to the EEPROM, then switching to
input mode to read the results. BTW this is the reason that you limit Data Out
instead of the PIC pin because you don't want data from Data Out being
presented to Data In while the PIC is still clocking in a command.

Hope this helps,

BAJ