Test circuitry implemented in an integrated circuit having a plurality of I/O circuits for testing of the electrical parameters of the I/O circuits without probing the contact pads associated therewith. The test circuitry includes a test drive bus, a test drive pad connected to the test drive bus, a test observe bus, a test observe pad connected to said test observe bus. Associated with each I/O circuit are a test drive transmission gate connected between the associated I/O pad and the test drive bus, and a test observe transmission gate connected between the associated I/O pad and the test observe bus. The transmission gates for each pad are controlled in parallel via a scan control register, and are connected by separate conductive traces to the I/O pad. If an I/O includes an input buffer, the input to the input buffer is connected to the I/O pad via the separate conductive trace to the test drive transmission gate; and if an I/O has an output driver, the output to the output driver is connected to the I/O pad via the separate conductive trace for the test observe transmission gate.