The 'ABTH18646A and 'ABTH182646A scan test devices with 18-bit bus transceivers and registers are members of the Texas Instruments SCOPETMtestability 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 bus transceivers and registers that allow for multiplexed transmission of data directly from the input bus or from the internal registers. 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 SCOPETMbus transceivers and registers.

Transceiver function is controlled by output-enable () and direction (DIR) inputs. Whenis low, the transceiver is active and operates in the A-to-B direction when DIR is high or in the B-to-A direction when DIR is low. Whenis high, both the A and B outputs are in the high-impedance state, effectively isolating both buses.Read more