Chapter 12. Test
12-23
BIST
7. Read (data)—compress (data)
8. Increment address and repeat for entire address space
9. Conduct self-pause
10.Release self-pause
11.Compare signature to stored signature value
12.Assert done and assert fail if necessary
The first pass through the ROM should begin at address 0. Each address location is read as
the test increments through the address space and captures the data in the MISR. The first
pass verifies the program data and the address decode.
The second read also starts at address 0 (step 6) and increments through the address. The
second read tests for any defects resulting from addressing or reading destructive reads. The
ROM is designed so that the golden comparison signature sets the MISR to a known value
(all zeros) at the end of the second read pass. The ROM signature is placed in the last
address (address max), so this value can be read during testing because it returns the
signature analyzer to its pretest state. The Version 4 ROM BIST logic assumes ROM array
dimensions of 32 bits by length L. At the conclusion of the reads, a fail flag is set if the
calculated signature does not match the golden signature.
NOTE:
A retention test is not required, but is in the Version 4 ROM
solution. HOLD mode pauses the ROM simultaneously with
other memory arrays. This allows memories to gracefully
remain in a quiescent state during data retention.
The scripts written in Section 12.3.6.1, “Modify BIST ROM Signature Script—Part 1,” and
Section 12.3.6.2, “Modify BIST ROM Signature Script—Part 2,” together create a
self-checking ROM signature value. The pseudo signature is the last line in the array.
Hence, the last line of the ROM cannot be used for functional purposes. When the BIST
MISR is applied to the ROM array, the final signature results in a value of all zeros if the
array has no errors. The script calculates the signature using the same algorithm, prime
polynomial of order 32, that the ROM BIST module uses. The prime polynomial used in an
N-bit polynomial is a N-bit binary expansion of a prime number that falls between 2
(N-1)
and 2
N
. Because of the math theorem that states that there is at least one prime number
between any numbers X and 2X, at least one prime number lies between 2
(N-1)
and 2
N
.
Motorola chose one of these prime numbers for the algorithm.
12.3.6.1 Modify BIST ROM Signature Script—Part 1
#############################################################
# FILE: modify_signature.sh
# DESCRIPTION:
# shell to modify N x 32 ROM last word (signature) for V4 ROM BIST. This shell
# takes as input a file name of the original ROM code, and creates a new file
# called by the original filename with “.modified” appended. This shell also
# diffs the two files.
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.