What Is a Programmable Logic Array?

Programmable array logic, English abbreviation PAL (programmable array logic). A programmable logic device consisting of a programmable and array, fixed or array and output feedback unit. PAL devices consist of programmable AND arrays, fixed or array and output feedback units. ^[1]

Programmable array logic

The output and feedback structure consists of a programmable array and a fixed or array. There is no output feedback signal. The input and output terminals are fixed and cannot be defined by the user. Only suitable for simple combinational logic circuit design.

Input and output structure

With tri-state output

PAL devices are fast, have low power consumption, and have multiple structure types, which can be used to design various combinational logic circuits and sequential logic circuits. The following aspects are mainly considered during design:
(1) The total number of input / output terminals of a PAL device is limited.
(2) The number of output product terms per PAL device is limited.
(3) In a PAL device with a register and a macrocell structure, when a register in a logic unit is used as an internal feedback register, a logic unit is required, and the corresponding output terminal cannot be used for other purposes; when the logic unit is used as a combination When outputting, it also occupies a logic unit, and its internal registers cannot be used.