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Browse Prior Art Database

LSSD Mapping Methodology

IP.com Disclosure Number: IPCOM000021135D
Original Publication Date: 2003-Dec-26
Included in the Prior Art Database: 2003-Dec-26
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Abstract

LSSD Mapping method that does not sacrifice test coverage used to require multiple bclocks. And the method that allows single bclock used to sacrifice test coverage. This invention suggests the method that does not either require multiple bclocks or sacrifice test coverage.

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LSSD Mapping Methodology

It is well known that especially when system clock or async-reset is generated inside

ASIC, in order to prevent racing condition multiple bclocks are needed. Fig.1 shows example circuit in which async-reset is generated inside chip and its wave form if single bclock(in the chart, ce1_b) is used. In this chart, spike occurs at the output of AND gates indicated by red dotted circle and that spike might cause malfunction of lssd latch during test. In order to solve this situation without losing test coverage, another bclock should be used. See Fig.2 below. Having multiple bclock usually forces us to have manual intervention during LSSD mapping, that is, full automated LSSD mapping is difficult or even impossible. Therefore, different mapping method which does not require multiple bclock is used. But that method loses test coverage.

Fig. 1

set

reset

ce0_se

systemclock

ce1_cs

ce1_cr

A

I C D

S

A

I C

datainD L2 ce1_c

B

R

dataout

A B

Z

B

ce1_b

Wave Form

Naming convention... ce1 = conformance enable 1 (Tied to 1 in normal operation) ce0 = conformance enable 0 (Tied to 0 in normal operation) ce1_c = cclock ce1_b = bclock ce0_se = scan enable (scangate)

A

ce1_b

Z

Fig. 2

Below chart shows the method that currently addopted. As indicated in this chart, although only one bclock is used, spike does not occur since cclock is always zero when bclock becomes active. But because of this, as it is shown in Fig.4 below, some stack fault cannot be detected.

1

set

reset

ce...