Thanks Ken, that was very helpful. The good news is that I got my system
working. The bad news is that I'm an idiot for missing something simple. I
spent so much time with the timing and commands that I neglected to read the
power section of the data sheet, and hence did not know to use the 4.7k
pull-up resistor. Ugh. Now I know, and it works.

Thanks again!

-Jeff

PS - the tip on using an extra I/O pin to broadcast an internal event is
great. I know I'll use that as I continue my adventures...

Quoting Kenneth Lumia <klumia@ADELPHIA.NET>:

> Jeff,
>
> The DS1820 is relatively simple to use.  For debugging:
>
> 0. Read the data sheet. Carefully.
>
> 1. Verify the hardware pinout.  Are you using parasitic
>     power or 5V?  If using parasitic power, the 5V pin
>     needs to be grounded, not floating.
>
> 2. Use a scope to verify timing.  You may want to use
>     a second pin and set it high to denote you are
>     transmitting, low to signify you are tri-state (floating,
>     waiting for the DS1820 to respond with presence
>     pulse and data).  Verify against the data sheet.
>     Note there are differences in timing between the earlier
>     DS1820 and the newer DS18S20.  You may want to
>     disable all unneeded code, no interrupts, etc. and just
>     use hardcoded delays as required. In other words,
>     simplify the environment as much as possible.  Are
>     you writing this in asm or 'C'?  Ensure that your delay
>     loops are really what you think they are (clock frequency
>     vs # of instructions in the delay - you may want to check
>     on a simulator (count cycles, time)).
>
> Ken

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