Texas Instruments Corporation

Yin-Chao Hwang

Theo J Powell

Jeffrey D Bellay

Martin D Daniels

A test circuit for a logic device having ports. The test circuit includes a serial scan path for serially transferring externally generated test vectors from a serial test input to a serial test output. A storing circuit stores a data bit and has a node at which the data bit is stored. A first interface circuit interfaces the node with a first one of the ports for synchronous transfer of data from the logic device to the node. A second interface circuit interfaces the node with the serial scan path to tranbsfer data from the serial scan path to the node. A coupling circuit connects the storing circuit to a second of the ports to transfer a logic level responsive to the data bit to the logic device during test. Also the coupling circuit temporarily couples the data bit from the node to the serial scan path also during test. A third interface circuit is provided for an asynchronous input of data from the logic device to the coupling circuit except during test wherein the asynchronous input is isolated from the coupling circuit. A control circuit controls the third interface and the coupling circuit during test in response to an external test enable signal. In this way, the second interface is operable during test to store data in the storing circuit for input to the logic device, and the first interface transfers test results from the logic device to the storing circuit for extraction through the serial scan path.

Test circuit and scan tested logic device with isolated data lines

A testable logic circuit includes parallel registers (72)-(80) for interfacing with a common internal bus (70). The parallel registers (72)-(80) are individually addressable by an address decoder (104) for storage of test vectors therein. These test vectors are then applied to associated logic circuits. Individual shift register latches (92)-(102) are provided at imbedded locations therein. The shift register latches are interfaced with a serial data link to allow serial loading of data therein. The parallel latches function in both the test mode to store test vectors for application to the associated logic and also in the operational mode for storage of logic data. Use of parallel registers increases the speed at which data is scanned into the device.

Parallel/serial scan system for testing logic circuits

A modularized scanned logic test system includes modularized logic circuits (26) having control/observation locations therein. Each of the control/observation locations has a shift register latch (SRL) disposed thereat. A common scan data in line (28) provides data to a serial input to each of the modules (26). The serial output of each of the modules (26) is interfaced with a scan data out line (30). An address on a bus (16) is provided to a decoder (52) to select one of the modules (26). An isolation gate (48) allows for input of data to only the select one of the modules (26) and an isolation gate (50) allows output of data only from the select one of the modules (26) to the scan data out line (30).

Modularized scan path for serially tested logic circuit

A transparent shift register latch (170) includes a normal operating gate (182) and a test gate (184) for selectively connecting data to a node (180). The node (180) is input to an isolation gate (186) through an inverter (188) for connection to an output node (190). A peripheral port (172) is interfaced with the output node (190) through an isolation gate (192). The gates (186) and (192) are operable in a test mode to interface data stored on the node (180) with the output of the latch (170) and inhibit input of data from the port (172). In the normal operating mode, the isolation gate (192) is closed and the isolation gate (186) is opened. The transparent shift register latch (170) allows testing of interface lines between adjacent logic modules.

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Sugar Land, TX, United States of America

Yin-Chao Hwang