>If you're going to be turning the power off then the tris register method
>won't work because the protection diodes in the unpowered PICs will draw
>power from the line.  Maybe the A4 pin could be used this way because it

Actually, if MCLR is tied directly to Vdd, the chip will start running,
drawing it's power from leakage through the i/o pins.

Your best bet is to use the TRIS registers to hi-z the pins while inactive.
 When active, you can make it even better by only turning only the pins
which are "0" states to output (and of couse setting the port to all 0's)
and permitting the weak pull-ups to take care of the rest.

Then you do a checksum-type calculation at the receiver to make sure you
got a good message.

This will prevent power zaps when two chips try to access the bus
simulataneously with different logic levels on a pin.

OOPS - I was thinking parallel xfers.  Same idea, though.  Kinda like I2C.

Andy

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Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865
          Hardware & Software for Industry & R/C Hobbies
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