Hardware Reference
In-Depth Information
the ECM (electronic control module or vehicle computer) under the dash. This chip contained
the vehicle operating software as well as all the data tables describing spark advance, fuel
delivery, and other engine and vehicle operating parameters. Many devices with integrated
computers use PROMs to store their operating programs.
Although we say these chips are blank when new, they are technically preloaded with binary 1s. In
other words, a 1Mb ROM chip used in a PC would come with 1 million (actually 1,048,576) bit
locations, each containing a binary 1. A blank PROM can then be programmed, which is the act of
writing to it. This usually requires a special machine called a device programmer, ROM programmer,
or ROM burner.
Programming the ROM is sometimes referred to as
burning
it because that is technically an apt
description of the process. You can think of each binary 1 bit as a fuse, which is intact. Most chips
run on 5 volts, but when a PROM is programmed, a higher voltage (normally 12 volts) is placed at
the various addresses within the chip. This higher voltage actually blows or burns the fuses at the
desired locations, thus turning any given 1 into a 0. Although you can turn a 1 into a 0, you should note
that the process is irreversible; that is, you can't turn a 0 back into a 1.
The device programmer examines the program you want to write into the chip and then selectively
changes only the 1s to 0s where necessary in the chip.
PROM chips are often referred to as
one-time programmable (OTP)
chips for this reason. They can
be programmed once and never erased. Most PROMs are inexpensive (about $3 for a typical PC
motherboard PROM), so if you want to change the program in a PROM, you discard it and program a
fresh one with the new data.
The act of programming a PROM takes anywhere from a few seconds to a few minutes, depending on
the size of the chip and the algorithm the programming device uses. A typical PROM programmer has
multiple sockets. This is called a
gang programmer,
and it can program several chips at once, saving
time if you have several chips to write with the same data. Less expensive programmers are available
with only one socket, which is fine for most individual use.
I use and recommend a programmer from a company called Andromeda Research Labs
(
www.arlabs.com
)
.
Custom Programming of PROM Chips
I even used a PROM programmer to reprogram the chip in an 1989 Turbo Trans Am, changing
the factory preset speed and rpm limiters, turbocharger boost, torque converter lockup points,
spark advance, fuel delivery, idle speed, and much more! I also incorporated a switch box
under the dash that enables me to switch from among four different chips, even while the
vehicle is running. One chip I created I called a “valet chip,” which, when engaged, cuts off the
fuel injectors at 36 miles per hour and restarts them when the vehicle coasts down to 35 mph.
Another chip I created cuts off fuel to the engine altogether, which I engage for security
purposes when the vehicle is parked. If you are interested in such a chip-switching device or
custom chips for your Turbo Trans Am or Buick Grand National, I recommend you contact
Casper's Electronics (
www.casperselectronics.com
).
EPROM
