<P> PALs and GALs are available only in small sizes, equivalent to a few hundred logic gates . For bigger logic circuits, complex PLDs or CPLDs can be used . These contain the equivalent of several PALs linked by programmable interconnections, all in one integrated circuit . CPLDs can replace thousands, or even hundreds of thousands, of logic gates . </P> <P> Some CPLDs are programmed using a PAL programmer, but this method becomes inconvenient for devices with hundreds of pins . A second method of programming is to solder the device to its printed circuit board, then feed it with a serial data stream from a personal computer . The CPLD contains a circuit that decodes the data stream and configures the CPLD to perform its specified logic function . Some manufacturers (including Altera and Microsemi) use JTAG to program CPLD's in - circuit from . JAM files . </P> <P> While PALs were being developed into GALs and CPLDs (all discussed above), a separate stream of development was happening . This type of device is based on gate array technology and is called the field - programmable gate array (FPGA). Early examples of FPGAs are the 82s100 array, and 82S105 sequencer, by Signetics, introduced in the late 1970s . The 82S100 was an array of AND terms . The 82S105 also had flip flop functions . </P> <P> FPGAs use a grid of logic gates, and once stored, the data doesn't change, similar to that of an ordinary gate array . The term "field - programmable" means the device is programmed by the customer, not the manufacturer . </P>

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