7.4 PROGRAMMABLE ARRAY LOGIC DEVICES 307
7.4 PROGRAMMABLE ARRAY LOGIC DEVICES
Perhaps the most widely used PLD is the programmable array logic (PAL) device. The
PAL device can be programmed only in the AND plane. For reference purposes the main
differences between ROMs, PLAs and PAL devices may be stated as follows:
ROM devices — Programmable in the OR plane only
PLA devices — Programmable in both AND and OR planes
PAL devices — Programmable in the AND plane only
Thus, a PLA device may be thought of as a combination of ROM and PAL device pro-
gramming characteristics. PAL devices, like PLAs, commonly include a variety of devices
external to their OR planes, including XOR gates, AND–OR–invert logic, and registered
outputs.
The acronym PAL is a registered ...