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Introducing Engineering Changes Externally in Read Only Memory Chip or Functional Chip

IP.com Disclosure Number: IPCOM000076435D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Singh, S: AUTHOR

Abstract

An approach to handle a certain number of engineering changes in read-only memory (ROM) chips or function chips is described. Unit logic chip or an appropriate semifunctional Engineering Change (EC) chip, which could be wired at the site for a required EC function, is connected with the original ROM or function chip in order to introduce the required engineering change.

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Introducing Engineering Changes Externally in Read Only Memory Chip or Functional Chip

An approach to handle a certain number of engineering changes in read-only memory (ROM) chips or function chips is described. Unit logic chip or an appropriate semifunctional Engineering Change (EC) chip, which could be wired at the site for a required EC function, is connected with the original ROM or function chip in order to introduce the required engineering change.

A typical circuit is shown in Fig. 1 having a function F. It is to be changed to a circuit shown in Fig. 2. Fig. 3 shows the Karnaugh plot for the original function F, F after EC, and the EC function for F. Notice that an EC function for any F is described by plotting changes on the Karnaugh map as 1's. It can also be represented with 0's (no change) in terms of the dual of an EC function, in case it becomes easier to realize it in the dual form.

When this EC function of F and original function F are exclusive ORed, then the output of the Ex-OR gate will realize a function after the engineering change. This is shown by the circuit schematic of Fig. 4.

The EC function is realized by a unit logic chip or more appropriately by a semifunctional chip of the type as shown in Fig. 5. This chip contains a number of small decoders and AND gates with maximum possible number of I/O's which can be accommodated. The final personality for the required EC function can be realized by interconnecting suitable I/O's only.

The abo...