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


----- Original Message -----
From: "Jeff Swayze" <jeff@FATSQUID.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, February 09, 2004 4:56 PM
Subject: [PIC]: PIC16F84A + Dallas DS1820 temp sensor = frustration


> I'm having problems interfacing a PIC16F84A with the Dallas 1-wire DS1820
> temperature sensor. There are several threads with some nice code, but
using
> those routines I still can't seem to get a good reading from the sensor.
My
> display routine constantly spits out a decimal "127".
>
> Instead of requesting more code, I was hoping the list could provide me
with
> some tips/pitfalls on using the sensor, and perhaps a strategy I could use
to
> inch my way through the debugging process. For instance, it would be nice
to
> know that I'm reading and writing data successfully or that my timing is
> correct.
>
> Any help for this "PIC newbie" (this is my first PIClist post) would be
greatly
> appreciated.
>
> -Jeff Swayze
> Cincinnati, OH
>
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