Chip information

[Mike Arman <armanmik@n-jcenter.com>]

>From: "Avram Dorfman" <dorfman@est.org>
>Subject: Re: Chip information
>
>Meck,
>
>Here is an answer to part of your question.
>
>There is no such thing as "modifying" a CPU or a chip - you either replace
>them or not. They are basically stamped out on a production line (ok, there
>are chemicals involved, etc). The chip mods that go into most cars are
>replacement ROMs, with different instructions for the CPU. There should be
>no reason to change the actual CPU, you would just be giving it a different
>program that has different priorities than thoes intended by Audi. It's not
>like having a faster CPU is going to enable your car to go faster.
>
>Disclaimer: This is based simply on chip theory - I don't claim to know for
>sure that there isn't a special situation going on in Audi computers that
>makes this different. It's conceivable that the ROMs and CPU are all on one
>board and have to be replaced together. If that's the case, and money could
>be gained by "salvaging" the old CPU, your only chance would be if the chip
>vendor offers you a core refund for sending in your old board, which my
>guess is they would do so they could pop off your old ROMs, replace them
>with their own & sell it to someone else.
>
>- -Avram
>

Avram, no. That's not correct.

The chip that is modified is an EPROM - electrically programmable read-only
memory. 

It is a large chip, usually 28 pins (the chip in a 5KQT is a 27C64), and it
has a quartz window in it through which you shine UV light to erase the
program on the chip. Then you use an EPROM "burner" to write the new
program onto the chip.

You are correct that the original chip cannot be modifed - there's no
window in it, and what you get is what you get. The 27C64 *IS*
re-programmable, and it is done ALL the time. The reason the vendors ask
for the complete computer is that the original chip is soldered in, and
must be removed so the EPROM can be fitted - hopefully into an added
socket, ideally into a ZIF (zero insertion force) socket.

I did a couple of chips for Todd Rooney some months ago, and he reported no
success. These chips are not totally reliable, and sometimes the EPROM
burner will tell you the chip is programmed correctly even when it isn't.
The chip itself is amazingly cheap - sometimes as little as 25 cents, in
quantity one, for a tested good used and erased pull. Be a sport - brand
new 27C64s are well under five bucks, and easily available.

Eprom burners cost as little as $99 (from Digi-Key - it's an add-on to your
computer - card plus outboard socket, somewhat clunky software included),
stand-alone units go for $600 or so, fancy ones the sky is the limit.

Best Regards,

Mike Arman