Browse Prior Art Database

Associative Storage Cell

IP.com Disclosure Number: IPCOM000077306D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Robinson, T: AUTHOR [+2]

Abstract

In an associative store the search field, by which a word is identified, does not usually overlap the read field in the same word. In some applications, such as character recognition, this leads to unnecessarily wide tables as not all bit positions of the search field are used to identify a word. The figure shows a conventional 4-state cell, comprising two bistables L and R, and modified so that it appears as a cell in the X state (don't care) during search but reads as a cell in the 1 state during read.

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Associative Storage Cell

In an associative store the search field, by which a word is identified, does not usually overlap the read field in the same word. In some applications, such as character recognition, this leads to unnecessarily wide tables as not all bit positions of the search field are used to identify a word. The figure shows a conventional 4-state cell, comprising two bistables L and R, and modified so that it appears as a cell in the X state (don't care) during search but reads as a cell in the 1 state during read.

The extra field-effect transistors (FETs) are referenced A, B, C, respectively. There is also an extra control line Read Y. To use the cell to store a read bit, it is set in the Y state, i.e. with the outer portions of L and R conductive. This would normally lead to a mismatch signal on the WORD SENSE line, irrespective of what search signals are placed on the lines DRIVE A to DRIVE D. However, FETs A and B block any search signal and the cell appears as if it were in the X state. During the read phase, if the word containing the cell has been selected, the READ Y line is activated which leads to a "1" - representing signal on the line SENSE. The Y state is detected by FET C. The cell also acts as a normal 3- state (1, 0, X) cell.

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