SN74ABT8646

The ’ABT8646 and scan test devices with octal 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 functionally equivalent to the ’F646 and ’ABT646 octal bus transceivers and registers. 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 normal mode does not affect the functional operation of the SCOPE™ octal 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 can be performed with the ’ABT8646.

In the test mode, the normal operation of the SCOPE™ bus transceivers and registers 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 as described in IEEE Standard 1149.1-1990.

Four dedicated test pins 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 pseudorandom pattern generation (PRPG) from data outputs. All testing and scan operations are synchronized to the TAP interface.

The SN54ABT8646 is characterized for operation over the full military temperature range of –55°C to 125°C. The SN74ABT8646 is characterized for operation from –40°C to 85°C.