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How to say which board was the first to detect a transition

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Full Member level 4
Jun 29, 2004
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Buenos Aires - Argentina
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PIC micro 16F family.

There are four boards, each one detecting the high to low transition in the eight pins of PORTB from the micro in charge, with weak pull ups enabled..

Depending of which board detects a change first, the rest should react differently to further changes in their "own" pins.

My question is: How could I make any of the boards to tell the others "I got a change in one of my pins", so the rest knows that they are not the first anymore in detecting a change?

I started to consider something like a common point for all boards, linking their open drain RA4 pins. What I can not see is how could I use that pin also for polling any change or signaling "mine was first" from the other boards.

Or should I use a second pin in every micro for the polling?.

My last point is: would all this change if I do it with three instead of four boards? A resistor, common to all of them or "distributed" should change value accordingly, I think.

To be honest I couldn't progress much in solving this. Help appreciated.

Re: How to say which board was the first to detect a transit


do you have an empty pin that you can use on each PIC?

because if you do

you can use a pin on each PIC to tell the others that either it got the data first (acting as o/p)

or this same pin changes to i/p at certain parts of the code to check if anyother board has sent a first response message

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