Complex programmable logic device


A complex programmable logic device is a programmable logic device with complexity between that of PALs and FPGAs, and architectural features of both. The main building block of the CPLD is a macrocell, which contains logic implementing disjunctive normal form expressions and more specialized logic operations.

Features

Some of the CPLD features are in common with PALs:
Other features are in common with FPGAs:
The most noticeable difference between a large CPLD and a small FPGA is the presence of on-chip non-volatile memory in the CPLD, which allows CPLDs to be used for "boot loader" functions, before handing over control to other devices not having their own permanent program storage. A good example is where a CPLD is used to load configuration data for an FPGA from non-volatile memory.

Distinctions

CPLDs were an evolutionary step from even smaller devices that preceded them, PLAs, and PALs. These in turn were preceded by standard logic products, that offered no programmability and were used to build logic functions by physically wiring several standard logic chips together.
The main distinction between FPGA and CPLD device architectures is that FPGAs are internally based on look-up tables while CPLDs form the logic functions with sea-of-gates.