At&t Bell Laboratories

At+t Corp.

At&t Ipm Corp.

Paul W Rutkowski

Eleanor Wu

John A Malleo-Roach

Chi W Yau

Najmi T Jarwala

William E Feger

A Boundary-Scan cell (12') for facilitating testing of an electronic device (10), includes a system flip-flop (30') interposed between an output buffer (18) of the device and an internal logic block (14) which drives the buffer. The system flip-flop has asynchronous clear and preset capability which allows the flip-flop to be cleared or preset as necessary so that its output bit reflects a bit previously latched in the Boundary-Scan cell during testing. During non-testing intervals, the preset and clear capability of the system flip-flop (30') is disabled to allow the flip-flop to pass a bit between the internal logic of the device and the output buffer without undue propagation delays.

Boundary scan cell

Pseudo-exhaustive self-testing of an electronic circuit (10), containing groups of combinational elements (14.sub.1,14.sub.2, 14.sub.3 . . . 14.sub.n), is accomplished by first partitioning the groups of combinational elements into sub-cones having no more than w inputs each by designating appropriate nodes ('test points') in each cone as the output of a sub-cone. A set of test vectors {a.sub.1, a.sub.2 . . . a.sub.w, b.sub.1, b.sub.2 . . . b.sub.w } is then generated (via an internal generator 74) such that when the vectors are applied to the sub-cones (14.sub.1.sbsb.a, 14.sub.1.sbsb.b . . . . 14.sub.i.sbsb.j), each sub-cone will be exhaustively tested. Each of the inputs of the sub-cones is assigned to receive a vector such that the vectors received at the inputs are linearly independent. The subset of vectors is applied through each of a plurality of pseudo-exhaustive self-test (PEST) flip-flop circuits (88) and through the test points to test the circuit. The PEST flip-flop circuits 88 also serve to advantageously compact and observe the response data produced by each sub-cone (14.sub.i.sbsb.j) with that of an upstream sub-cone.

Pseudo-exhaustive self-test technique

Psuedo-exhaustive self-testing of an electronic circuit (10), containing groups of combinational elements (14.sub.1, 14.sub.2, 14.sub.3 . . . 14.sub.n), is accomplished by first partitioning the groups of combinational elements into sub-cones having no more than w imputs each by designating appropriate nodes ('test points') in each cone as the output of a sub-cone. A set of test vectors {a.sub.1, a.sub.2 . . . a.sub.w, b.sub.1, b.sub.2 . . . b.sub.w } is then generated (via an internal generator 74) such that when the vectors are applied to the sub-cones (14.sub.1.sbsb.a, 14.sub.1.sbsb.b . . . . 14.sub.i.sbsb.j), each sub-cone will be exhaustively tested. Each of the inputs of the sub-cones is assigned to receive a vector such that the vectors received at the inputs are linearly independent. The subset of vectors is applied through each of a plurality of pseudo-exhaustive self-test (PEST) flip-flop circuits (88) and through the test points to test the circuit. The PEST flip-flop circuits 88 also serve to advantageously compact and observe the response data produced by each sub-cone (14.sub.i.sbsb.j) with that of an upstream sub-cone.

A method is disclosed for generating a control signal (TMS) which may be used to control the test activity of boundary scan system (10). The method is initiated by loading a multi-bit control macro (STI, DTI or DSTI) into a register (38) whose output is coupled back to its input. After loading of the macro, its identity is ascertained by a macro controller (42) which serves to decode a multi-bit signal (IT) whose state is indicative of the macro type. The macro controller (42) actuates the register to shift out the bits of the control macro in a sequence dependent on the macro's identity in order to generate the appropriate control signal. As each bit is shifted out, it is shifted back into the register so as to allow the same sequence of bits to be repeatedly shifted out.

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Morris Plains, NJ, United States of America

Paul W Rutkowski