PIC Odometer - not so long :)

[Frederic Breitwieser]

>for anyone interested in the PIC odometer code I sent out the other day,
>here is a text file that goes into some
>detail of how the code works.

One of the things I was working on, then abandoned, was to build a 64HCxxx
ECM, much like the 332 project going on (I dropped it as not to reduplicate
efforts), but was going to utilize a simple trick to store live, changing
data such as engine sensor history, error codes, and of course, the
odometer.  Instead of using a simple dynamic or static RAM chip, where the
data is wiped gone when power is removed, I was going to use the Dallas
Semiconductor 2764 replacement chip (8K by 8 bits), which is a 10 year
lithium powered memory chip, which has the same pinouts as the 2764 eprom,
to store all the working data.  When its powered up, the data lives and
stays :)  Originally I was going to use it in place of the EPROM code I was
going to write, so I could reprogram it easily without the ultraviolet
burning crap, then I realized, hey, why not store everything in it?

Compaq had used these for years in their EISA machines, where the PC box
has to store its EISA configuration for the rest of the PC to utilize,
whether power is on or off, which is where I got the idea from.

The 2764 replacement is Dallas part number #DS-1225Y-170

I was trying to figure out the best way to clock the miles as the GM
computer I'm using (currently) doesn't like the Audi transaxle, and at the
time, I didn't have the ability to create a simple circuit to generate the
4000 ppm (or so) that the ECM was expecting.


Frederic Breitwieser
Bridgeport, CT 06606

Homebrew Automotive Website:
http://www.xephic.dynip.com/

"When in doubt, use a bigger hammer"
-