From: Justin Richards <justin.richards@gmail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Fri, 5 Jun 2020 01:06:05 -0700
Subject: Re: [EE] Detecting a change of level on four lines with digital
	logic/analog circuitry?
Thread-Topic: [EE] Detecting a change of level on four lines with digital
	logic/analog circuitry?
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Base on "The four signals can change at any time to any direction " then I
must assume that 2 or more lines may transition at precisley the same time.

Is that a correct assumption.

Justin

On Fri, Jun 5, 2020 at 4:38 AM Jason White <
whitewaterssoftwareinfo@gmail.com> wrote:

> Hi everyone,
>
> I have an application where I need to generate at pulse least 1 microseco=
nd
> long any time a rising or falling edge is detected on four digital lines.
> The four signals can change at any time to any direction. The pulse is us=
ed
> to trigger a timer providing a reset signal to the rest of the system.
> Microcontrollers and programmable logic devices aren't allowed.
>
> Four 74HC123s will do it, but are too big.
> Four window comparators monitoring the signal through an RC will do it, b=
ut
> also seems too big.
>
> Is four schmitt trigger XOR gates with four RC's the smallest
> implementation?
>
> I was thinking some sort of analog implementation might be able to do it
> smaller. But AC coupling the four signals together would allow them to
> cancel out. Perhaps a 4-bit encoder/decoder or multiplexer might do it
> better?
>
> Regards,
> Jason White
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