A 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 programmed.

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.

Using a ROM as a PLD

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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 $2^m$ 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 $2^m$ 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.

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ajkk (ajkk) Fri, 06 Nov 2009 11:56:03 -0000
[bkmk] http://3.ly/c0X - Programmable logic innovation is overdue ＞ メモ
Of course Programmable Logic Arrays and Programmable Array Logics would be completely different pieces of hardware. Thanks world!
melonhead901 (Kellen D) Wed, 04 Nov 2009 07:33:48 -0000
Of course Programmable Logic Arrays and Programmable Array Logics would be completely different pieces of hardware. Thanks world!
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korshynez (Ксения Коршунец) Tue, 03 Nov 2009 17:50:52 -0000
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BrownbookUpdate (Dave and Marc) Tue, 03 Nov 2009 11:57:20 -0000
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Microchip introduces resistor-programmable logic-output temperature switches: Microchip has announced the MCP95.. http://bit.ly/1NPo35
angliaComponent (Anglia Components) Tue, 03 Nov 2009 09:01:58 -0000
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