SCANSTA112 datasheet(8/15 Pages) NSC

8 / 15 page

Application Overview (Continued)

such a configuration, the system tester can configure the

local ports of a set of ’STA112s so as to connect a specific

set of local scan-chains to the active scan chain. Using this

capability, the tester can selectively communicate with spe-

cific portions of a target system. The tester’s scan port is

connected to the backplane scan port of a root layer of

’STA112s, each of which can be selected using multi-drop

addressing. A second tier of ’STA112s can be connected to

this root layer, by connecting a local port (LSP) of a root-

layer ’STA112 to the backplane port of a second-tier

’STA112. This process can be continued to construct a multi-

level scan hierarchy. ’STA112 local ports which are not cas-

caded into higher-level ’STA112s can be thought of as the

terminal leaves of a scan tree. The test master can select

one or more target leaves by selecting and configuring the

local ports of an appropriate set of ’STA112s in the test tree.

STANDARD SCANBRIDGE MODE - ScanBridge mode re-

fers to functionality and protocol that has been used by

National since the introduction of the PSC110 in 1993. This

functionality consists of a multidrop addressable IEEE1149.1

switch. This enables one (or more) device to be selected

from many that are connected to a parallel IEEE1149.1 bus

or backplane. The second function that ScanBridge mode

accomplishes is to act as a mux for multiple IEEE1149.1

local scan chains. The Local Scan Ports (LSP) of the device

creates a connection between one or more of the local scan

chains to the backplane bus.

To accomplish this functionality the ScanBridge has two

levels of protocol and an operational mode. Level 1 protocol

refers to the required actions to address/select the desired

ScanBridge. Level 2 protocol is required to configuring the

mux’ing function and enable the connection (UNPARK) be-

tween the local scan chain and the backplane bus via an

LSP. Upon completion of level 1 and 2 protocols the Scan-

Bridge is prepared for its operational mode. This is where

scan vectors are moved from the backplane bus to the

desired local scan chain(s).

STITCHER MODE - Stitcher Mode is a method of skipping

level 1 and 2 protocol of the ScanBridge mode of operation.

This is accomplished via external pins. When in stitcher

mode the SCANSTA112 will go directly to the operational

mode.

TRANSPARENT MODE - Transparent mode refers to a

condition of operation in which there are no pad-bits or

SCANSTA112 registers in the scan chain. The Transparent

mode of operation is available in both ScanBridge and

Stitcher modes. Only the activation method differs. Once

transparent mode has been activated there is no difference

in operation. Transparent mode allows for the use of vectors

that have been generated for a chain where these bits were

not included.

Check with your ATPG tool vendor to ensure support of

these features.

For details regarding the internal operation of the SCAN-

STA112 device, refer to applications note AN-1259 SCAN-

STA112 Designers Reference.

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