From jcwren@atlanta.com Tue Mar  4 20:55:52 1997
Date: Sun, 02 Mar 1997 18:09:10 GMT
From: John Wren <jcwren@atlanta.com>
To: 8051code@keil.com
Subject: DS1820 Code Bug

    I found a minor bug in the Dallas DS1820 temperature sensor
code I posted the other day, that has to do with a sensor not
responding.  If no sensor is connected to the I/O pin, and it is
pulled either internally or externally, everything works fine.
However, if the I/O pin is grounded (sensor fault or wiring fault),
the code will think a sensor is present, and report the temperature as
0 degrees.

    The problem lies in the code that checks for the assertion of
the presence pulse from the sensor.  It only verifies that the sensor
drives it low, and not that it was high prior to being driven low.  

    I haven't fixed this yet, but as soon as I do, I'll post a
code fix.  Better yet, if someone else fixes it, I'd like to be sure
to get the fix to pull into my code.

        - John

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