Ok, skipping all the off-topic stuff.
Maxim/Dallas's one wire parts use the phrase "strong pullup" to
indicate the line SHOULD BE DRIVEN HIGH. The pullup resistor is not
enough, a PIC's weak pullups is not enough, the combination is not
enough. The specs vary across the product range, but holding 90% of
Vcc at 10mA is a good place to start.
This is only necessary for the parasite powered parts, and only during
certain times (like doing a conversion or writing to EEPROM).

Some of the data sheets show an external FET controlled from another
output pin to do this, many people have successfully toggled the TRIS
bit and used the PIC to drive it high, including myself.


It's been a while since I had my head in that code, but as I recall
there's a certain time limit. Strong pullup _must_ be active within a
certain time of issuing the command. It bit me on the backside because
I had about 10 sensors to watch and the software had several nested
calls to manage them all. In the end I had to separate out a couple of
the routines to meet the timing requirement.

-Denny
--=20
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