At 14:46 16/05/97 -0400, Carlton Haycock wrote:
>I am relatively new to PIC's.  Using a part like the PIC16C84, what would be
>the most straight forward way to interface to the TMP04 temperature sensor?
>The TMP04 is a 3-wire device (+5v,gnd,data_out).  The temperature is encoded
>using ratiometric encoding.  Basically what is done is that the data_out line
>is held high for a certain period of time (T1) and held low for a certain
>period of time (T2) and this repeats, over and over.  To read the
>temperature, you
>measure the times T1 & T2 and plug them into the following formula:
>
>F degrees = 455 - ((T1*720)/T2) (if memory serves....)
>
>Anyway, I need to find the least complicated scheme to measure the two times
>T1 and T2.  I have looked at the sensor on a scope and manually calculated
the
>temperature and it was very close.  The average timing is 35hz, so it is not
>very high speed.

Since the c/f84 don't have any fancy timer stuff, but have these
interrupt-on-change port b (bits 4..7), I'd probably put it on one of these
and on interrupt read the timer value. (You have to make sure that you take
care of the timer overflows: either handle them in a timer ov interrupt
routine, effectively creating a 16bit timer, or make sure the timer runs
slow enough to not overflow twice between two port interrupts.) The rest is
simple math, it seems.

(I have only _very_ limited and still mostly theoretical PIC knowledge... :-)