| US 7,454,664 B2 | ||
| JTAGchain bus switching and configuring device | ||
| Mike Conrad Duron, Pflugerville, Tex. (US); Robert Allan Faust, Austin, Tex. (US); Forrest Clifton Gray, Austin, Tex. (US); Ajay Kumar Mahajan, Austin, Tex. (US); and Glenn Rueban Miles, Austin, Tex. (US) | ||
| Assigned to International Business Machines Corporation, Armonk, N.Y. (US) | ||
| Filed on Jun. 30, 2003, as Appl. No. 10/610,170. | ||
| Prior Publication US 2005/0015669 A1, Jan. 20, 2005 | ||
| Int. Cl. G06F 11/00 (2006.01) | ||
| U.S. Cl. 714—43 [714/27; 714/30; 714/45; 714/51] | 4 Claims |
| 1. 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.
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