Apparatus for JTAG-driven remote scanning

摘要

A scan circuit (JTAG 1149 extension) for a microprocessor utilizes transport logic and scan chains which operate at a faster clock speed than the external JTAG clock. The transport logic converts the input serial data stream (TDI) into input data packets which are sent to scan chains, and converts output data packets into an output data stream (TDO). The transport logic includes a deserializer having a sliced input buffer, and a serializer having a sliced output buffer. The scan circuit can be used for testing with boundary scan latches, or to control internal functions of the microprocessor. Local clock buffers can be used to distribute the clock signals, controlled by thold signals generated from oversampling of the external clock. The result is a JTAG scanning system which is not limited by the external JTAG clock speed, allowing multiple internal scan operations to complete within a single external JTAG cycle.

主权项

1. A scan circuit for a semiconductor device having one or more functional units, comprising:
at least one scan chain which interconnects multiple scan cells embedded in the one or more functional units, said scan chain being controlled by an internal clock signal having a first frequency; a scan interface including a scan input and a scan output, said scan interface being controlled by an external clock signal having a second frequency which is slower than the first frequency; first transport logic which passes an input serial data stream representing pattern data from said scan input to said scan chain; and second transport logic which passes an output serial data stream from said scan chain to said scan output.