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US 7,454,664 B2Granted
JTAGchain bus switching and configuring device
AssigneeInternational Business Machines Corporation
InventorsMike Conrad Duron, Robert Allan Faust, Forrest Clifton Gray, Ajay Kumar Mahajan, Glenn Rueban Miles
Life of this patent
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Abstract
Commanding a JTAG bus cross point switching device by the same bus which it configures. Adding, omitting, or rearranging devices on a JTAG bus with a cross point switching device that is included in a JTAG chain. Controlling the switching device with commands on the JTAG bus which it configures.
Claims4
A method of configuring a Joint Test Action Group (JTAG) bus, comprising the steps of:
- powering up a cross point switch that is connected to the JTAG bus, wherein the cross point switch responds to commands issued on the JTAG bus, and wherein the cross point switch is configured by a command that is issued on the JTAG bus, and further wherein the switch includes a JTAG input and a JTAG output, and still further wherein a plurality of devices are connected to the JTAG bus;
- omitting, by the cross point switch, all of said plurality of devices from the JTAG bus when the cross point switch is powered up;
- responsive to the cross point switch being powered up, issuing, by a bus controller that is connected to the JTAG bus, a first command to the cross point switch to connect all of said plurality of devices to the JTAG bus;
- connecting, by the cross point switch, all of the plurality of devices to the JTAG bus in response to the first command;
- responsive to a fault occurring in one of said plurality of devices, issuing a second command to reset all connections to omit all of said plurality of devices from said JTAG bus;
- omitting, by the cross point switch, all of said plurality of devices from the JTAG bus in response to said second command;
- and
- shorting the JTAG input and the JTAG output in response to all of said plurality of devices being omitted.
5 more elements
Dependencies are inferred from the claim text.