In article <4e34s3$ok5@nyx.cs.du.edu> slindsay@nyx.cs.du.edu (Steve Lindsay) writes:
>From: slindsay@nyx.cs.du.edu (Steve Lindsay)
>Subject: Help with design
>Date: 23 Jan 1996 10:11:31 -0700
>I have eight external lines any one of them can be high or
>low (+5v high or 0v low). When any one of them change
>state I would like another line to break connection for just a
>very short time and then reconnect. The reconnect part
>has to be automatic. (It will be causing a hardware
>interrupt). This one line needs to reconnect right away
>before any of the other lines change state. The eight lines
>will change state at about 5000 blips a sec.
>Anyone have any ideas what I could do this with? Is there
>a chip that will take in eight inputs and if any change it
>would output something happened on just one line?
>Any ideas for the reconnect part for the interrupt line? It
>needs to do switching. It would normally be closed but
>when it was told to open it would only open and then shut
>right away automatically.
>Thanks for any help!
What you can use to detect a line-change is the following:
__
line o---------\\ \
| __ || >-----> to 8-input nor-gate
-|__|---//__/
| exclusive-or gate
---
---
|
___
///
I think the resistor can be something like 10K, the capacitor 4.7nF
So each line needs one ex-or gate, one capacitor and one resistor.
The idea is that a line-change will make the inputs of the ex-or to differ
from each other for a short time (about 50 microseconds), and the resulting
High-pulse on the output can be nor'd (or you could even use 8 diodes for a
wired-or. I don't really understand what you mean by breaking and reconnecting
the interrupt line; most interrupt lines need to be pulled down or something
like that to generate an interrupt. Here that can easily be accomplished by
using a transistor after the 8-input or- or nor-gate.
Success,
Richard
Richard Rasker
Calslaan 54-11
7522 MG Enschede
Holland
tel. +31-(0)53-4350834
Date: Thu, 25 Jan 1996 13:33:04 UNDEFINED
Original Subject: Re: Help with design