[Free] Old Data Books (Australia)

Ethan Dicks ethan.dicks at gmail.com
Tue Sep 4 22:41:25 CDT 2007


On 9/4/07, Roy J. Tellason <rtellason at verizon.net> wrote:
> > GAL16V8A / 15LP / L218D16
>
> I've no direct experience with these,  but have heard of "GAL" chips,  sort of
> like "PAL" chips is about all that comes to mind offhand.

GALs and PALs are similar devices, with a few key differences... PALs
are bipolar devices, and are programmable once.  GALs are made of
newer technologies, like FLASH or EAROMs, thus can be erased and
reprogrammed a number of times.  PALs come in pre-coded flavors like
10L6 or 16H2, meaning 10 inputs with 6 low-true outputs or 16 inputs
and 2 high-true outputs.  With PALs, you took a fistful of your
equations, then you, yourself, picked a part in which the equations
would fit.  To make a complex product, you might have 6 or 8 or 10
flavors of PALs in the same design.  GALs are "Generic Arrayed Logic",
thus are not pre-configured for certain geometries.  A small part
would routinely be described as a 16V8, meaning _up to_ 16 inputs and
_up to_ 8 outputs, with Versatile choice of high true or low true for
the outputs (also there were "registered" PALs like the 16R4 with
flip-flops on the outputs for clocking or latching - GAL outputs are
also optionally "registered").

In the early 1980s, PALs were popular because one PAL could replace a
dozen TTL parts.  GALs became popular because you only had to stock
one type of 18-pin part, one type of 20-pin part, one type of 24-pin
part, etc., rather than well over a dozen non-interchangable,
non-reprogrammable parts.  Eventually, even GALs were too simplistic
for most professional product designs, but they are still popular with
hobby projects - look at the Spare Time Gizmos line to see how easy it
is to make GAL-based projects.  GALs are still readily available for
$1 or less. I don't think they've made PALs in a large number of years
(not that there aren't still millions of loose parts on the resale
market).

Hope that illuminates more than obscures,

-ethan



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