PLA vs PAL: Key Differences in Programmable Logic Arrays
PLA (Programmable Logic Array) is a digital circuit whose AND and OR arrays can both be programmed; PAL (Programmable Array Logic) fixes the OR array and lets you program only the AND array.
Designers blur them because both sit in the same drawer, look alike on schematics, and share “programmable” in the name—yet mixing them up can turn a sleek prototype into a board that won’t fit or over-heats.
Key Differences
PLA gives two levels of programmability—custom product terms and custom sums—so you can fold more logic into one chip. PAL is simpler: you get many product terms but a fixed sum, trading flexibility for speed and lower cost.
Which One Should You Choose?
Need dense, multi-function glue logic with relaxed timing? Pick PLA. Racing for MHz in a cost-sensitive gadget? Grab a PAL. Most hobbyists reach for PAL first; PLA shines when board space and power trump unit price.
Examples and Daily Life
Retro gaming mods often use a PAL to decode cartridge addresses at 5 V; a satellite modem’s baseband card hides a PLA that merges half-dozen state machines into one low-power core.
Can I swap a PLA for a PAL in an old arcade board?
No—the fixed OR plane in PAL breaks the original PLA equations, causing glitches or silence.
Are PLAs still manufactured today?
Most are obsolete; engineers migrate to CPLDs or FPGAs, though specialty houses still make military-grade PLAs.