SCAN TEST DEVICES WITH 18-BIT TRANSCEIVERS AND REGISTERS

The ABTH18646A and ABTH182646A scan test devices with 18-bit Bus Transceivers and Registers 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 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 SCOPE Bus Transceivers and Registers Transceiver function is controlled by output-enable (OE) and direction (DIR) inputs. When OE is 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. When OE is high, both the A and B outputs are in the high-impedance state, effectively isolating both buses. Data flow is controlled by Clock (CLKAB and CLKBA) and select (SAB and SBA) inputs. Data on the A bus is clocked into the associated Registers on the low-to-high transition of CLKAB. When SAB is low, real-time A data is selected for presentation to the B bus (transparent mode). When SAB is high, stored A data is selected for presentation to the B bus (registered mode). The function of the CLKBA and SBA inputs mirrors that of CLKAB and SAB, respectively. Figure 1 shows the four fundamental bus-management functions that are performed with the ABTH18646A and ABTH182646A. By Texas Instruments