Control circuitry is coupled between an error event output and a data input of a pseudorandom binary sequence (PRBS) checker. The control circuitry is configured to switch between a first operating state in which a received PRBS signal is applied to the data input of the PRBS checker and a second operating state in which an error signal is applied to the data input of the PRBS checker, responsive to detection of a designated condition of the PRBS checker. In an illustrative embodiment, the designated condition is an end-of-test condition indicating that the PRBS checker has completed a test involving the received PRBS signal.