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# Marching Test Improvement for RAM Built-In Self Test

IP.com Disclosure Number: IPCOM000040623D
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 38K

IBM

## Related People

Carval, JL: AUTHOR [+2]

## Abstract

This article describes an original way to entirely apply any Marching Test Algorithm to all the cells of any given RAM independent of the number of data inputs (DIs) and the number of addresses of the product. The Marching Test Algorithm is generally applied only to the RAM addresses, so each N bit word of the RAM (N = number of DI) is considered as an elementary cell for the algorithm. Therefore, any coupling fault between cells of the same RAM word cannot be detected. So the Marching Test Algorithm is not completely applied to the product, and some of the potential electrical faults would not be detected. To improve the test effectiveness, the idea is to consider the RAM DI as address complement. Then, for a RAM with M addresses and N Date inputs, the 2M x N Bit word RAM becomes a N x 2M x 1 bit word RAM.

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Marching Test Improvement for RAM Built-In Self Test

This article describes an original way to entirely apply any Marching Test Algorithm to all the cells of any given RAM independent of the number of data inputs (DIs) and the number of addresses of the product. The Marching Test Algorithm is generally applied only to the RAM addresses, so each N bit word of the RAM (N = number of DI) is considered as an elementary cell for the algorithm. Therefore, any coupling fault between cells of the same RAM word cannot be detected. So the Marching Test Algorithm is not completely applied to the product, and some of the potential electrical faults would not be detected. To improve the test effectiveness, the idea is to consider the RAM DI as address complement. Then, for a RAM with M addresses and N Date inputs, the 2M x N Bit word RAM becomes a N x 2M x 1 bit word RAM. Any Marching Test Algorithm requires reading and writing into the memory in ascending and descending order. Unlike the sequencer logic dedicated to the RAM addresses where a simple counter/decounter can be used thanks to the RAM decoder, the increment and decrement operation applied on the RAM DI must be built in a different manner (because there is no RAM decoder for the DI). In the diagram, the control input CNTRL may take two values: a 1 for the ascending order and a 0 for the descending order. Data inputs are comprised of: DATA A, Data value which is loaded into the SRL step by step and DATA B, Data valu...