Datasheet

SCANSTA112
SNLS161I –DECEMBER 2002–REVISED APRIL 2013 www.ti.com
APPLICATION OVERVIEW
ADDRESSING SCHEME
The SCANSTA112 architecture extends the functionality of the IEEE 1149.1 Standard by supplementing that
protocol with an addressing scheme which allows a test controller to communicate with specific 'STA112s within
a network of 'STA112s. That network can include both multi-drop and hierarchical connectivity. In effect, the
'STA112 architecture allows a test controller to dynamically select specific portions of such a network for
participation in scan operations. This allows a complex system to be partitioned into smaller blocks for testing
purposes. The 'STA112 provides two levels of test-network partitioning capability. First, a test controller can
select individual 'STA112s, specific sets of 'STA112s (multi-cast groups), or all 'STA112s (broadcast). This
'STA112-selection process is supported by a Level-1 communication protocol. Second, within each selected
'STA112, a test controller can select one or more of the chip's seven local scan-ports. That is, individual local
ports can be selected for inclusion in the (single) scan-chain which a 'STA112 presents to the test controller. This
mechanism allows a controller to select specific scan-chains within the overall scan network. The port-selection
process is supported by a Level-2 protocol.
HIERARCHICAL SUPPORT
Multiple SCANSTA112's can be used to assemble a hierarchical boundary-scan tree. In 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 specific
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 cascaded 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 refers to functionality and protocol that has been used 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) between the local scan chain and the
backplane bus via an LSP. Upon completion of level 1 and 2 protocols the ScanBridge 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 SCANSTA112 device, refer to applications note AN-
1259(SNLA055) SCANSTA112 Designers Reference.
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