PLA & PAL devices

Describe PLA & PAL in detail?

PLA is a device with programmable AND array and programmable OR array. However in PAL, the programmable array logic is a fixed OR array and a programmable AND array. Because only AND array is programmable, the PAL is easy to program. But it is less flexible than PLA.

Some PALs have flip-flops at the output. The flip-flops store the outputs. Together these flip-flops can serve as a register. Generally, these flip-flops have tristate buffers, hence the output of the registers can easily be controlled. The flip-flop outputs are made available as input to be used in generation of additional product terms. This feedback feature allows PALs to be used for design of counters, registers and sequential controllers.