Page 202 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

Programmable ICs R 7 83
a b c

AND Array
W X Y

Figure 16-7. AND array feeding
into an OR array

core PLD concepts are relatively simple, the wider arena may
prove to be a morass of confusion to the unwary. There are a multiplicity of
PLD alternatives, most of which seem to have acronyms formed from different
combinations of the same three or four This may be, as some suggest, a
strategy to separate the priests from the acolytes, or it may be that the inventors
of the devices had no creative energy left to dream up meaningful names for
them. Whatever the case, the more common PLD variants are introduced
below.

Programmable Logic Arrays (PLAs)
The most user-configurable of the traditional PLDs are programmable logic
arrays (PLAs) ,7 because both the AND and OR arrays are programmable
(Figure 16-8).

6 A common engineering joke is to refer to TLAs, which is an acronym that stands for “three
letter acronyms” (in conversation, TLA is pronounced by spelling it out as “T-L-A”).
7 In conversation, PLA is spelled out as “P-L-A.”