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Browse Prior Art Database

PLA with Product Term Test Circuit

IP.com Disclosure Number: IPCOM000052374D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Chu, WM: AUTHOR [+2]

Abstract

A programmable logic array (PLA) can be personalized by making laser welds at selected crosspoints of the array. A circuit test is made after each product term is personalized and all other product terms are temporarily deleted. Some of the product terms in the OR array apply data to a latch which performs a logical AND function. The data content of the latch can be monitored either at the primary output or through the LSSD scan path. However, the inputs to the latch can not be tested at the PLA output because a signal that might be applied by the product term line for test is inhibited by the 0 logic state of each other input to the AND function. An auxiliary circuit provides a supplemental input to the AND latch on the associated product term lines so that a coincidence of signals permits testing these product terms.

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PLA with Product Term Test Circuit

A programmable logic array (PLA) can be personalized by making laser welds at selected crosspoints of the array. A circuit test is made after each product term is personalized and all other product terms are temporarily deleted. Some of the product terms in the OR array apply data to a latch which performs a logical AND function. The data content of the latch can be monitored either at the primary output or through the LSSD scan path. However, the inputs to the latch can not be tested at the PLA output because a signal that might be applied by the product term line for test is inhibited by the 0 logic state of each other input to the AND function. An auxiliary circuit provides a supplemental input to the AND latch on the associated product term lines so that a coincidence of signals permits testing these product terms.

The drawing shows representative product term lines and a latch that performs an AND function on the inputs from two lines. Dots at crossover points of row and column lines represent welds that provide a connection from an input on a row line to an output along a column line. In addition to these standard components, the PLA includes several auxiliary test product term lines that have pre-established connections to each of the column lines. To test a weld at crossover point 2, pulses are applied to product term line 3 and to the auxiliary line 4 to satisfy the AND function of the latch, and the output of the latch...