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Programmable Test Point

IP.com Disclosure Number: IPCOM000047552D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Malone, JP: AUTHOR

Abstract

One important consideration in the design of logic cards that contain buried oscillators involves the inclusion of a test point therefor. This point is used during card test to measure and verify the output parameters of the buried oscillator. However, the use of such a test point may lead to unwanted oscillations on a possible long wire and the potential for radio frequency interference (RFI). This problem can be overcome, or greatly reduced, by using the circuit below. Oscillator 1 normally feeds logic circuits 2 on the same card. The AND gate implemented circuit 3 will normally block the oscillator output to test point (TP) 2. This insures that there is no oscillator signal present on line 7 during normal (non-test) operation. For test purposes, TP 1 is taken to a logical "0" which pulls down the input to the AND gate.

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Programmable Test Point

One important consideration in the design of logic cards that contain buried oscillators involves the inclusion of a test point therefor. This point is used during card test to measure and verify the output parameters of the buried oscillator. However, the use of such a test point may lead to unwanted oscillations on a possible long wire and the potential for radio frequency interference (RFI). This problem can be overcome, or greatly reduced, by using the circuit below. Oscillator 1 normally feeds logic circuits 2 on the same card. The AND gate implemented circuit 3 will normally block the oscillator output to test point (TP) 2. This insures that there is no oscillator signal present on line 7 during normal (non-test) operation. For test purposes, TP 1 is taken to a logical "0" which pulls down the input to the AND gate. This allows the oscillator output now to be measured at TP 2, thereby making that point location programmable for testing purposes. Distance "a" should be kept as short as practical to reduce the potential for RFI problems.

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