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What is Run-Test/Idle State?

The run-test/idle state is a TAP controller state where once entered, the controller state will remain as long as the test mode state (TMS) is held low. In the run-test/idle state, only certain instructions are available. For example, the RUNBIST instruction causes a self test of the boundary scan device system logic to execute.

For instructions that do not cause functions to execute in the run-test/idle state, the test data registers selected by the current instructions will retain their previous state.

IEEE 1149.6 and IEEE 1532 standards use the run-test/idle state extensively to control operation related to programming and testing of boundary scan devices.