I've implemented some 1-Wire code to read a DS18B20 sensor using a PIC, using 
parasite power.  Still in testing on a breadboard, it sits there all day with 
2 sensors on the bus reading ~28 deg C.  But periodically, perhaps once every 
few hours, I get an odd value of "85", or "-21" once interpreted from the 
DS18B20's format.  Seemingly important, this works out to B'10101010', and 
even more important is that it passes the checksum test.

I can now reproduce this by removing the positive power from the sensor.  And 
it's always that magic "85".  Is there some significance to this, so that I 
can figure out how to determine it's bogus and not display 85?  I can't find 
any reference to this value or bit pattern being generated when power to the 
chip is lost or otherwise.  That it's passing the checksum test is really 
bothering me.

Cheers,
-Neil.



-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist