Patent ID: 7319936

Claim:
An instrument for an automatic test system in which a communication link carries messages, comprising: a) an interface comprising: i) a reference clock input; ii) a port to connect to the communication link; b) a clock generator, the clock generator coupled to the reference clock input and receiving a reference clock from the reference clock input and outputting a local clock; c) a timing circuit, clocked by the local clock, having an input to receive a value representative of a time and an output, the timing circuit asserting the output at a time represented by the value received at the input; d) a message processing circuit having an input coupled to the port and an output coupled to the input of the timing circuit; wherein the timing circuit includes a time-tracking sub-circuit that counts pulses of the local clock; and wherein the timing circuit comprises at least one comparator circuit having an output coupled to the output of the timing circuit, the comparator having a first input coupled to the output of the message processing circuit and a second input coupled to the time-tracking sub-circuit.