> 1) If I use intrc can I still use the UART ???

This is strictly a matter of timing tolerance between the two devices on the
line.  The receiver looks for the leading edge of the start bit, then times
the other bits relative to that.  At 8 data bits, the center of the last bit
is 8 1/2 bits from the leading edge of the start bit.  The absolute maximum
tolerable error is therefore 5.88%, which causes the last data bit to be
sampled at its edge instead of the middle.  Most receivers sync everything
to a 16x baud clock, so there is an additional small uncertainty in
measuring the leading edge of the stop bit.  Of course, you don't want to be
near the guaranteed to fail limit anyway.  I like to see no more than about
1/4 bit time error by the last bit, or about 3% clock mismatch betwen
receiver and transmitter.

Keep in mind that this is the combined error between receiver and
transmitter.  If you know the other end is right on (like a PC, for
example), then you can get away with 3% mismatch in the PIC.  If you've got
two PICs with uncertain oscillators, then they each need to be within 1.5%.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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