A test system 100 that can accept a plurality of plug-in electronic cards in Xi Slots 126 or PXI slots 134 is described. The test or source measure switching system 100 includes a sequencer or sequence engine 130 which is fully capable of executing opcode instructions having potentially indefinite completion times and monitoring multiple asynchronous inputs simultaneously without interrupts. The sequencer 130 is sequential and deterministic to approximately ten microsecond resolution.