Tri-State Mode

In a test environment, the processor can be configured to disconnect from (i.e., to tri-state its output drivers on) all of its output pins. This permits an external board tester to drive all of the signal traces (normally driven by the processor) to known values. Using a bed-of-nails fixture that permits probing of all system board nodes, the board tester can then verify that all of these signal traces are properly connected to all of the appropriate nodes on the board.

The processor is configured to tri-state all of its output drivers when it samples a low on its SMI# pin at the trailing-edge of reset. This function used to be assigned to the processor's FLUSH# input, but FLUSH# was eliminated starting with the Pentium® 4 processor.