Shadow access port method and apparatus
AssigneeTexas Instruments Incorporated
InventorLee D. Whetsel
Life of this patent
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Abstract
The disclosure describes a novel method and apparatus for providing a shadow access port within a device. The shadow access port is accessed to perform operations in the device by reusing the TDI, TMS, TCK and TDO signals that are used to operate a test access port within the device. The presence and operation of the shadow access port is transparent to the presence and operation of the test access port. According to the disclosure, the shadow access port operates on the falling edge of the TCK signal while the test access port conventionally operates on the rising edge of the TCK signal.
Claims20
An electrical device comprising;
- (a) device terminals including functional input terminals, functional output terminals, a TDI input terminal, a TMS input terminal, a TCK input terminal, and a TDO output terminal;
- (b) functional circuitry coupled to the functional input terminals and coupled to the functional output terminals;
- (c) a first access port circuit having a data input coupled to the TDI input terminal, a control input coupled to the TMS input terminal, a clock input coupled to the TCK input terminal, a data output, and a first enable output;
- (d) a second access port circuit having a data input coupled to the TDI input terminal, a control input coupled to the TMS input terminal, a clock input coupled to the TCK input terminal, a data output, and a second enable output;
- and
- (e) an output control circuit having a first data input coupled to the data output of the first access port circuit, a second data input coupled to the data output of the second access port circuit, a first enable input coupled the first enable output, a second enable input coupled to the second enable output and a data output coupled to the TDO output terminal.
A device comprising:
- a test data in (TDI) input terminal;
- a test mode select (TMS) input terminal;
- a test clock (TCK) input terminal;
- a test data out (TDO) output terminal;
- a first access port circuit configured to operate according to Institute of Electrical and Electronics Engineers (IEEE) standard 1149.1, wherein the first access port circuit includes:
- a data input coupled to the TDI input terminal;
- a control input coupled to the TMS input terminal;
- a clock input coupled to the TCK input terminal;
- a data output;
- and
- a first enable output;
- a second access port circuit configured to operate apart from the IEEE standard 1149.1, wherein the first access port circuit includes:
- a data input coupled to the TDI input terminal;
- a control input coupled to the TMS input terminal;
- a clock input coupled to the TCK input terminal;
- a data output;
- and
- a second enable output;
- and
- an output control circuit including:
- a first data input coupled to the data output of the first access port circuit;
- a second data input coupled to the data output of the second access port circuit;
- a first enable input coupled the first enable output;
- a second enable input coupled to the second enable output;
- and
- a data output coupled to the TDO output terminal.
Dependencies are inferred from the claim text.