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Triple Bit Coding

IP.com Disclosure Number: IPCOM000077308D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Jones, JW: AUTHOR

Abstract

Function tables held in associative stores can be shortened if search inputs are coded before application to the table as a search argument. In triple-bit coding, three input bits are coded to address two columns of four state cells such as C1 or C2. Each cell has two bistables L and R, each connected to a respective column line. All bistables of the same word are connected to a word line W. The four states of a cell are 0: L = 1, R = 0; 1: L = 0, R = 1; X: L = 0, R = 0: and Y: L = 1, R = 1. Negative logic is used, as represented in Fig. 1 by the inverters 10. The existence of a condition is represented by the lowering of a column line.

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Triple Bit Coding

Function tables held in associative stores can be shortened if search inputs are coded before application to the table as a search argument. In triple-bit coding, three input bits are coded to address two columns of four state cells such as C1 or C2. Each cell has two bistables L and R, each connected to a respective column line. All bistables of the same word are connected to a word line W. The four states of a cell are 0: L = 1, R = 0; 1: L = 0, R = 1; X: L = 0, R = 0: and Y: L = 1, R = 1. Negative logic is used, as represented in Fig. 1 by the inverters 10. The existence of a condition is represented by the lowering of a column line. If a column line is not lowered and a bistable to which the line is connected is in the one state, a mismatch signal is generated on the word line W which causes the word not to be selected for accessing.

The three input bits E, F, G, are coded according as their decimal sum is or is not greater than one and is or is not odd. If the sum is greater than one, the left column line of C1 is marked and if it is odd the left column line of C2 is marked. Selective masking of each column of the store is provided as well as masking of each E, F or G bit. For reading, the Even column line gives the output E bit, the Odd line gives the F bit and the >1 line gives the G bit.

Fig. 2 shows a four-bit, three-operand add table such as might be used for computation of base plus displacement plus index. The search field is represented by the states of the C1 and C2 bistables as defined above. Blanks represent bistables in the X state, although X states embedded in the table have been shown. The read field has been simplified so as to show only the result...