Browse Prior Art Database

Using Verified RAM to Test ROM on the Same Chip

IP.com Disclosure Number: IPCOM000115264D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Cheung, MH: AUTHOR

Abstract

A method for testing a ROM in a processor chip with an already verified RAM in the same chip is disclosed. This method identifies the first failing ROM address logged in a register to be scanned from the chip afterwards.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Using Verified RAM to Test ROM on the Same Chip

      A method for testing a ROM in a processor chip with an already
verified RAM in the same chip is disclosed.  This method identifies
the first failing ROM address logged in a register to be scanned from
the chip afterwards.

      Since contents of ROM are usually incorporated into chip
silicon during chip mask build process and remains unchanged are from
there on, any changes detected to be different from the original ROM
contents indicates the ROM to be defective.  As long as a processor
chip's RAM has been verified to be working via on chip memory self
test hardware like Array Built In Self Test (ABIST), the known ROM
contents can be loaded into the RAM via scanning method or written
into the RAM directly through chip primary input pins used as data
bus.  Usually a processor chip's RAM has at least the same amount of
memory addresses as the ROM or even more in most cases, therefore
loading the whole ROM contents into the RAM should not be a problem.
As far as the width of the RAM (i.e., number of data bits each row of
RAM has) is concerned, it has to be the same as the width of the ROM
or longer.

      The only on chip test hardware needed to test out the ROM is a
set of exclusive OR gates used for comparing the actual ROM contents
read from the ROM and the known to be good ROM contents loaded into
the RAM as mentioned in last paragraph, and lastly a register to hold
the failing ROM address that is first detected.  To incr...