-----Original Message-----
From: Bryson, William G (Bill) <BRYSOWG@TEXACO.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Thursday, September 18, 1997 07:34
Subject: Talking/reading To/From 4 pics serially...



>I have a project that requires 4 16C84 pics to receive data from one
>source
>serially.  That is to say the Port B lines would have to be either
>connected
>directly together or via a OR series of gates.  The premise is that I
>want the
>4 pics to be listening for commands sent by one common radio and then
>subsequently one would wake up when its ID code was detected and then
>respond to the command by doing its task.  After the task is completed
>then
>it would send back serially via radio through one common Xmit line
>connected
>to all 4 pics.  Can I connect the pics received and xmit lines up
>directly together
>or should I isolate them all from each other via CMOS LOGIC chips?
>
>I have one main controller Pic #1 that will be controlling the power of
>each of the
>other 3 Pics.  So the controller Pic #1 is turned on by DTR on a reset
>line.  It reads
>the initial traffic.  If Pic #2 is needed to do a task Pic #1 turns on
>the power to
>Pic #2 and then Pic #2 goes into listen mode.  The radio traffic is
>sent.  Pic #2 reads
>it and does its task and sends the response back via radio.  Pic #1 is
>told via radio
>to shut down Pic #2's power.
>
>I have read some threads in this list that talk of drawing power from
>other pins
>even though power is off on the Pic #2, Pic #3 and Pic #4.  Is this a
>concern in
>this application?  Or should I just isolate everything via CMOS logic?
>I need to turn
>off the power of the other 3 Pics to conserve power.  Pic #1 is the only
>Pic that
>will always have power and be ether sleeping or awake. Thanks for your
>help...

    I suggest you read up on the I2C standard, it does precisely this, more
than one master. You have to use the open collector outputs on the pic you
use, if available, if not you will have to use other CMOS logic as a buffer.
TTYL