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Fail Safe Storage Cell

IP.com Disclosure Number: IPCOM000090215D
Original Publication Date: 1969-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Duke, KA: AUTHOR [+2]

Abstract

The fail-safe cell fails with both outputs at the same prespecified value 0,0 or 1,1, depending on the choice of the logic used for the output gates. The circuit consists of two latches which are set independently, either in-phase or out-of-phase, at nominally the same time. The outputs of the latches are fed to two gate circuits, one output from each latch to each gate, so chosen that the two inputs to each gate have nominally the same logic value.

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Fail Safe Storage Cell

The fail-safe cell fails with both outputs at the same prespecified value 0,0 or 1,1, depending on the choice of the logic used for the output gates. The circuit consists of two latches which are set independently, either in-phase or out-of- phase, at nominally the same time. The outputs of the latches are fed to two gate circuits, one output from each latch to each gate, so chosen that the two inputs to each gate have nominally the same logic value.

As long as the two latches operate correctly, the gates have different outputs. When a failure occurs such that one latch differs from its nominal value, the gates have identical outputs. The gates can be And's, Or's, Nand's or Nor's depending on the fail-safe state required. If both gates are And's or if both gates are Nor's, they are chosen from the class of biased-failured circuits to be fail-to-0 circuits. If both gates are Nand's or if both gates are Or's, they are chosen from the class of biased-failure circuits to fail-to-1

Assume G1 and G2 are And's and that F2 fails. It is assumed that it fails to one of the two states a2, b2 = 0,1 or 1,0 and be stuck in that state for all values of its inputs x2,y2. First let F2 fail to the 0,1 output. If a1,b1 = 1,0, then z1,z2 = 1,0. If a1,b1 = 0,1, z1,z2 = 0,0 and the failure is indicated by the 0,0 output. Second let F2 fail to the 1,0 output. If a1,b1 = 0,1, then z1,z2 = 1,0. However, if a1,b1 = 1,0, then z1,z2 = 0,0 and the failure is indicated...