The SN74BCT8373 scan test device with octal D-type latches is a member of the Texas Instruments SCOPETM 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, this device is functionally equivalent to the SN74F373 and SN74BCT373 octal D-type latches. The test circuitry can be activated by the TAP to take snapshot samples of the data appearing at the device terminals 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 SCOPETM octal latches. In the test mode, the normal operation of the SCOPETM octal latches is inhibited and the test circuitry is enabled to observe and control the I/O boundary of the device. When enabled, the test circuitry can perform boundary-scan test operations as described in IEEE Standard 1149.1-1990. Four dedicated test terminals 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. The SN74BCT8373 is characterized for operation from 0C to 70C.