Method 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 method of scanning pattern data into a scan chain which interconnects multiple scan cells embedded in one or more functional units of an integrated circuit, comprising:
receiving an external clock signal from a source outside the integrated circuit at a scan interface of the integrated circuit, the external clock signal having first frequency; receiving an input serial data stream representing the pattern data at an input of the scan interface of the integrated circuit; passing the input serial data stream from the input of the scan interface to the scan chain as shift data using first transport logic; shifting the shift data through the scan chain controlled by an internal clock signal to generate return data, the internal clock signal having a second frequency which is faster than the first frequency; and passing the return data from the scan chain to an output of the scan interface as an output serial data stream using second transport logic.