On Tue, 1 Nov 2005, James Newton, Host wrote:

> So what is the minimum number of micro pins to hook up 8+ bits of input AND
> output via shift registers? E.g. one parallel input shift out and one shift
> in parallel out. They can share the clock, but not latch and data so that is
> 5 lines, but there should be some clever way to reduce that count.

If you can afford the extra time simply daisy chain input and output 
registers (not necessarily grouped). Minimum to drive is 1 clock/strobe 
and 2 data IO pins (1O 1I). This requires the dodgy RC strobe derivation 
from clock gaps. Add one more pin for proper strobe and it's 4 pins.

Imho by the time you need a lot of IO it may make sense to use another 
low cost PIC for that, as slave, on RC clock.

Peter
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