Path: utzoo!attcan!uunet!samsung!dali.cs.montana.edu!milton!wiml
From: wiml@milton.u.washington.edu (William Lewis)
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: Using a PC to monitor an external signal (How?)
Message-ID: <4767@milton.u.washington.edu>
Date: 5 Jul 90 02:47:46 GMT
References: <1990Jul4.215014.29212@mintaka.lcs.mit.edu>
Organization: University of Washington, Seattle
Lines: 23

In article <1990Jul4.215014.29212@mintaka.lcs.mit.edu> streeter@im.lcs.mit.edu (Kenneth B. Streeter) writes:
>I would like to use an ibm pc to monitor an external signal.  The
>signal in question is from a single digital wire.  The signal on the
>wire is essentially a square wave, from 0V to 5V, with an irregular
>period.  The input signal frequency would never be above about 150 Hz.

   Since the signal is already nice, digital and 0-5 volts, you could try
just hooking it up to a parallel or serial port status line, and then
polling this line 300 times a second or whatever. Since this is in a car,
an opto-isolator might be a good idea too.
   The problem is that this would take most of the pc's time just polling
the line for worst-case behavior. It might be possible to hook it up to
the receive line on the serial port, and have the hardware generate
an "incoming character" interrupt on rising edges. The ISR could simply
increment a counter in memory somewhere, and the logger (or whatever
is looking at the info) could check this periodically.
   For a first try, you could connect it to the "busy" pin of the parallel
port (pin 11 on a Centronics connector) and use service 2 of int 23 to
poll it.

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