Newsgroups: sci.electronics,comp.robotics
Path: cantaloupe.srv.cs.cmu.edu!rochester!udel!news.mathworks.com!bigboote.WPI.EDU!news3.near.net!analog.com!pmi.analog.com!johng
From: johng@pmi.analog.com (John Guy)
Subject: Re: How to get 128 bits of digital I/O the easy way?
Message-ID: <1995May19.192908.5165@analog.com>
Sender: usenet@analog.com
Organization: Precision Monolithics, Analog Devices
References: <D8LMpI.EBE@stardust.oau.org> <3p81sb$9qo@fermat.mayo.edu> <D8qDxC.Myr@stardust.oau.org>
Date: Fri, 19 May 1995 19:29:08 GMT
Lines: 32
Xref: glinda.oz.cs.cmu.edu sci.electronics:133097 comp.robotics:20905

In article <D8qDxC.Myr@stardust.oau.org>, kc4zvw@stardust.oau.org (David Billsbrough) writes:
|> Jim Craighead wrote:
|> 
|> > >I would like to implement at least 64 bits of input and 64 bits of output
|> > >on an embedded controller as a project.  I thought of using a 'heap' of
|> > >82C55 PIA chips but does anybody else have an easier or cheaper solution?
|> > 
|> >  There are easier/different ways, but they are dependant on your application.
|> > Why do you need 128 bits of I/O?
|> 
|> This device is to be a programmable continuity checker and would be controlled
|> by a host computer.  I wanted to use a microcontroller, instead of a plug-in
|> board for the PC's ISA bus, so that it could be used with non-PC and laptop
|> machines.  I would be using the serial interface to 'talk' with the host
|> computer and the host would request which bit is to be set and would receive 
|> binary numbers from the controller with which bits were 'high' on the input 
|> port.
|> 
|> I would prefer to use a 8051 family microcontroller but the 68HC11 has not
|> been ruled out.
|> 
|> // David //
|> -- 
|> David Billsbrough
|> kc4zvw@stardust.oau.org

You should use a microcontroller with an ADC internal, then use 
a CMOS analog multiplexer, 16 to 1 (I think CD4067). The circuit would require
5 of these chips. Additionally, using a total of 9 of these, you 
could use them as demultiplexors, and verify not only the continuity,
but also the exclusive connection of each pin, as well as get an idea
for the Ron of the selected channel (within the tolerance of the Ron of the MUX)
