More Info (was Re: HP 2100S microcode blanks?) MMI 63S140

From: Eric Smith <eric_at_brouhaha.com>
Date: Fri Feb 4 02:57:32 2005

Bruce wrote:
> Curiousity: Is it not possible to replace the bipolar devices with
> something a little more modern, available, and less expensive?
>
> Case in point: Motorola made a radio several years ago (the MCX100 and
> the Syntor series) that depended on 82S131's for their program memory.
> When those chips started getting scarce, a company called Brinkley
> Electronics came out with a neat little widget that consists of a 28C16
> EEPROM mounted on an adapter board to fit into a 16-pin DIP socket to
> make for a pin-to-pin replacement for the bipolar device.

The main problem is timing. Most bipolar PROMs are 55 ns or faster, and
most EPROMS, EEPROMS, and Flash memory parts are 70 ns or slower. Likely
the Motorola radio wasn't designed to take advantage of the speed of
bipolar PROMs.

Cypress made a line of CMOS PROMs intended to replace the bipolars, but
now they're only pushing them for replacement purposes in military
equipment, so the prices tend to be over $100 each. This makes it hard
for me to sympathize too much with complaints about paying over $5 each
for NOS bipolar PROMs.

The really small bipolar PROMs such as the 82S23 and 82S123, which are
32 words of 8 bits, can usually (but not always) be replaced by a PAL
or GAL on a pinout adapter.

The only practical current replacement for larger fast bipolar PROMs is
high-speed flash memory. SST makes many parts in 512Kbit and up that
have 55 ns read access time. They also have 45ns parts in 1 Mbit and
up. There are some faster parts, but they mostly are not 5V tolerant
and/or have unusual interfaces.

Eric
Received on Fri Feb 04 2005 - 02:57:32 GMT