The 'ABTH18502A and 'ABTH182502A scan test devices with 18-bit
universal bus transceivers are members of the Texas Instruments SCOPE
testability integrated-circuit family. This family of devices
supports IEEE Standard 1149.1-1990 boundary scan to facilitate
testing of complex circuit-board assemblies. Scan access to the test
circuitry is accomplished via the 4-wire test access port (TAP)
interface.
In the normal mode, these devices are 18-bit universal bus
transceivers that combine D-type latches and D-type flip-flops to
allow data flow in transparent, latched, or clocked modes. They can
be used either as two 9-bit transceivers or one 18-bit transceiver.
The test circuitry can be activated by the TAP to take snapshot
samples of the data appearing at the device pins or to perform a self
test on the boundary-test cells. Activating the TAP in the normal
mode does not affect the functional operation of the SCOPE universal
bus transceivers.
Data flow in each direction is controlled by output-enable ( and ), latch-enable (LEAB and LEBA),
and clock (CLKAB and CLKBA) inputs. For A-to-B data flow, the device
operates in the transparent mode when LEAB is high. When LEAB is low,
the A-bus data is latched while CLKAB is held at a static low or high
logic level. Otherwise, if LEAB is low, A-bus data is stored on a
low-to-high transition of CLKAB. When is low, the B outputs are active.
When is high, the B
outputs are in the high-impedance state. B-to-A data flow is similar
to A-to-B data flow but uses the , LEBA, and CLKBA inputs.
In the test mode, the normal operation of the SCOPE universal bus
transceivers is inhibited and the test circuitry is enabled to
observe and control the I/O boundary of the device. When enabled, the
test circuitry performs boundary-scan test operations according to
the protocol described in IEEE Standard 1149.1-1990.
Four dedicated test pins observe and control the operation of the
test circuitry: test data input (TDI), test data output (TDO), test
mode select (TMS), and test clock (TCK). Additionally, the test
circuitry performs other testing functions such as parallel-signature
analysis (PSA) on data inputs and pseudo-random pattern generation
(PRPG) from data outputs. All testing and scan operations are
synchronized to the TAP interface.
Improved scan efficiency is accomplished through the adoption of a
one boundary-scan cell (BSC) per I/O pin architecture. This
architecture is implemented in such a way as to capture the most
pertinent test data. A PSA/COUNT instruction also is included to ease
the testing of memories and other circuits where a binary count
addressing scheme is useful.
Active bus-hold circuitry holds unused or floating data inputs at
a valid logic level.
The B-port outputs of 'ABTH182502A, which are designed to source
or sink up to 12 mA, include 25- series resistors to reduce overshoot and undershoot.
The SN54ABTH18502A and SN54ABTH182502A are characterized for
operation over the full military temperature range of -55°C to
125°C. The SN74ABTH18502A and SN74ABTH182502A are characterized
for operation from -40°C to 85°C.
A-to-B data flow is shown. B-to-A data flow is similar but
uses OEBA\, LEBA, and CLKBA.
Output level before the indicated steady-state input
conditions were established
