US Patent 7406641 Selective control of test-access ports in integrated circuits

To facilitate testing, some integrated circuits include built-in test circuits, called test-access ports (TAPs). The present inventor recognized that TAPs are sometimes used with automatic testers that have limitations, such as insufficient memory capacity, that make it difficult or costly to test some integrated circuits, such as microprocessors. Accordingly, this disclosure teaches, among other things, inputting test signals to a TAP of an integrated circuit using a first device, such as an automatic tester, and outputting state data related to the input test signals from the TAP using a second device.