In article <4e34s3$> (Steve Lindsay) writes:
>From: (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.



 Richard Rasker
 Calslaan 54-11
 7522 MG  Enschede 
 tel. +31-(0)53-4350834

Date: Thu, 25 Jan 1996 13:33:04 UNDEFINED

Original Subject: Re: Help with design

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