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Home > Programmable logic device

It is impossible to discuss PLD technology without mentioning some of the companies involved in its development. However, it is not the purpose of this article to list all manufacturers of PLDs. Inclusion or omission of a particular company from this article is intended as neither a recommendation nor a criticism.

1 Using a ROM as a PLD

Before PLDs were invented, read-only memory (ROM) chips were used to create arbitrary combinatorial logic functions of a number of inputs. Consider a ROM with m inputs (the address lines) and n outputs (the data lines). When used as a memory, the ROM contains words of n bits each. Now imagine that the inputs are driven not by an m-bit address, but by m independent logic signals. Theoretically, there are possible Boolean functions of these m signals, but the structure of the ROM allows just n of these functions to be produced at the output pins. The ROM therefore becomes equivalent to n separate logic circuits, each of which generates a chosen function of the m inputs.

The advantage of using a ROM in this way is that any conceivable function of the m inputs can be made to appear at any of the n outputs, making this the most general-purpose combinatorial logic device available. Also, PROMs (programmable ROMs), EPROMs ( ultraviolet-erasable PROMs) and EEPROMs (electrically erasable PROMs) are available that can be programmed using a standard PROM programmer without requiring specialised hardware or software. However, there are several disadvantages: they are usually much slower than dedicated logic circuits, they consume more power, and because only a small fraction of their capacity is used in any one application, they make an inefficient use of space. Also, they cannot easily be used for sequential logic, because they contain no flip-flops.

2 Early programmable logic

Main article: Programmable array logic.

The first programmable logic devices for the commercial market were introduced by Monolithic Memories, Inc.(MMI) under the name of PAL ( Programmable array logic), although IBMThis article is about the International Business Machines Corporation; see IBM (disambiguation) for other uses of this abbreviation. International Business Machines Corporation IBM or colloquially, Big Blue (incorporated June 15, 1911, in operation since produced similar devices for internal use in the mid-1970s.

After MMI succeeded with the 20-pin PAL parts, AMDFor other possible meanings of AMD see AMD (disambiguation Advanced Micro Devices, Inc. AMD ( NYSE:AMD) is a manufacturer of integrated circuits based in Sunnyvale, California. It is the second-largest supplier of x86 compatible processors, and a leading introduced the 24-pin 22V10 PAL with additional features. After buying out MMI (1987?), AMD spun off a consolidated operation as Vantis, and that business was acquired by Lattice SemiconductorLattice Semiconductor Corporation is a leading manufacturer of high-performance programmable logic devices (PLDs), Field-programmable gate arrays (FPGAs) and related software. Lattice was incorporated in Oregon in 1983 and reincorporated in Delaware in 19 in 1999.

3 GALs

An innovation of the PAL was the generic array logic device, or GAL, invented by Lattice Semiconductor Inc. This device has the same logical properties as the PAL but can be erased and reprogrammed. The GAL is very useful in the prototyping stage of a design, when any bugsA computer bug is an error, flaw, mistake, failure, or fault in a computer program that prevents it from working correctly or produces an incorrect result. Bugs arise from mistakes and errors, made by people, in either a program's source code or its desig in the logic can be corrected by reprogramming. GALs are programmed and reprogrammed using a PAL programmer.

A similar device called a PEEL (programmable electrically erasable logic) was introduced by the International CMOS Technology (ICT) corporation.

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Programmable logic controllerPLC A programmable logic controller PLC or programmable controller is a small computer used for automation of real-world processes, such as control of machinery on factory assembly lines. Where older automated systems would use hundreds or thousands of re Programmable read-only memoryA programmable read-only memory PROM is a memory that comes blank, the contents of each bit is determined by a fuse or antifuse. The memory can be programmed once after manufacturing by "blowing" the fuses (using a PROM blower , which is an irreversible p Programmable logic deviceA programmable logic device or PLD is an electronic component used to build digital circuits. Unlike a logic gate, which has a fixed function, a PLD has an undefined function at the time of manufacture. Before the PLD can be used in a circuit it must be p Programmable logic arrayA programmable logic array (PLA is a programmable device used to implement combinational logic circuits. The PLA has a set of programmable AND planes, which link to a set of programmable OR planes, which can then be conditionally complemented to produce a Programmable array logicProgrammable array logic (PAL is a programmable logic device used to implement combinational logic circuits. The PALs were the first programmable logic devices for the commercial market, introduced by Monolithic Memories, Inc. The PAL, in comparison to th Programmable Universal Machine for AssemblyThe PUMA P rogrammable U niversal M achine for A ssembly, or P rogrammable U niversal M anipulation A rm) was a robot-arm system developed by Vic Schienman at MIT for General Motors. Unimation produced PUMAs for years until being purchased by Westinghouse