A testing device uses an input signature register to conduct "at speed" testing
of asynchronous circuit responses in an effort to determine the operability of
a monitored circuit. Upon receiving an enable signal, the input signature register
quickly measures, compresses, and transmits the tested circuit responses so that
the responses can be compared with a set of anticipated responses to determine
whether the circuit is functioning properly. The enabled input signature register,
such as a MISR or a SISR, generates an output signature, which contains the compressed
responses of the monitored circuit and helps the testing device analyze circuit performance.
