Browse Prior Art Database

Read Only Store Design

IP.com Disclosure Number: IPCOM000074680D
Original Publication Date: 1971-May-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Tang, CK: AUTHOR

Abstract

Reduction in the number of storage cells required for the masking procedure in the design of a read only memory (ROS) to provide a substantial reduction in cost is achieved by the following technique.

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Read Only Store Design

Reduction in the number of storage cells required for the masking procedure in the design of a read only memory (ROS) to provide a substantial reduction in cost is achieved by the following technique.

A ROS of n inputs can be represented by a function F of n variables i(1),--- ,i(n). This function F is first expanded with respect to all of its variables to obtain a standard sum of the products form as follows:

(Image Omitted)

Each of the terms in the above has two parts. The first part is a decode output and the second part is a residue function which is either 0 or 1. This equation describes the personalizations (as indicated by the respective base connections) of a conventional current switch ROS design as shown in Fig. 1 for n=8. 2/n/storage cells (transistors in current switch ROS) are required corresponding to the 2/n/ products in Equation (1).

The same function is expanded with respect to n-1 of its n variables as follows:

(Image Omitted)

There are only 2/n-1/ products in the equation. A current switch ROS of n variables can be constructed according to this equation using only 2/n-1/storage cells (half of the conventional requirement) as shown in Fig. 2 (for n=8). The * in Fig. 2 indicates the connection to an appropriate residue function of the single variable i(8). Thus four signal lines, not shown, carrying four logical values 0,1,i(8),i(8) should be provided in the ROS array, and the connection from each base to one of these four...