Member of the Texas Instruments

Widebus Family

UBT Transceiver Combines D-Type

Latches and D-Type Flip-Flops for

Operation in Transparent, Latched, or

Clocked Mode

Compatible With IEEE Std 1149.1-1990

(JTAG) Test Access Port (TAP) and

Boundary-Scan Architecture

Includes D-Type Flip-Flops and Control

Circuitry to Provide Multiplexed

Transmission of Stored and Real-Time Data

Two Boundary-Scan Cells (BSCs) Per I/O

for Greater Flexibility

SCOPE Instruction Set

– IEEE Std 1149.1-1990 Required

Instructions, Optional INTEST, and

P1149.1A CLAMP and HIGHZ

– Parallel Signature Analysis (PSA) at

Inputs With Masking Option

– Pseudorandom Pattern Generation

(PRPG) From Outputs

– Sample Inputs/Toggle Outputs (TOPSIP)

– Binary Count From Outputs

– Device Identification

– Even-Parity Opcodes

description

The SN74ABT18502 scan test device with an 18-bit universal bus transceiver is a member of the

Texas Instruments SCOPE testability IC family. This family of devices supports IEEE Std 1149.1-1990

boundary scan to facilitate testing of complex circuit board assemblies. Scan access to the test circuitry is

accomplished via the four-wire test access port (TAP) interface.

In the normal mode, this device is an 18-bit universal bus transceiver that combines D-type latches and D-type

flip-flops to allow data flow in transparent, latched, or clocked modes. The device 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 (OEAB and OEBA), 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 OEAB is low, the

B outputs are active. When OEAB 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 OEBA, 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 Std 1149.1-1990.

Four dedicated test pins are used to 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 can perform

other testing functions such as parallel signature analysis (PSA) on data inputs and pseudorandom pattern

generation (PRPG) from data outputs. All testing and scan operations are synchronized to the TAP interface.

Additional flexibility is provided in the test mode through the use of two boundary-scan cells (BSCs) for each

I/O pin. This allows independent test data to be captured and forced at either bus (A or B). A PSA/binary count

up (PSA/COUNT) instruction is also included to ease the testing of memories and other circuits where a binary

count addressing scheme is useful.