Abstract: In circuit testers, notably automatic test equipment for the in circuit testing of digital devices, overheating damage can result if outputs are repeatedly "overdriven", that is, while applying a test input to a first device, an output of a second connected device is forced into a state contrary to that it would normally adopt. Damage is avoided by enforcing a cooling interval between overdriving tests based upon a list of parameters representative of the overdriven device and its environment. In order to reduce the overall test time, a parameter is based on a measurement derived from a circuit of the type under test. A first test results in device heating to a value. A cooling interval is enforced so that a subsequent test which results in further heating of the device, may be made without exceeding device maximum allowable temperature .sup.T max.

Abstract: During the testing of circuit boards with Automatic Test Equipment in some circuit configurations the performance of a component may not be as expected even though it is sound due to the influence of surrounding components. In such a situation guards may be placed, that is further signals via probes contacting nodes other than those to which the component is connected, so that such disruption may be minimized. A method for defining guards during the operation of automatic test equipment so that a selected component of a circuit may be tested includes establishing a measurement of the selected component in a known to be good circuit of the type to be tested. A circuit node associated with the selected component is identified and a guard is applied to the node. A second measurement is established with the selected guard in place. If the guard results in an improvement, it is retained during subsequent automatic testing.

Abstract: In automatic test equipment the logical levels on certain of the test pins are set to 0 and 1 by corresponding flip-flops included in respective I/O logic circuits. The states of the flip-flops (as well as other factors) are controlled by commands read out of a control RAM which is of sufficient width to provide a 4-bit command on lines for each logic circuit. The available commands include NOP commands and change commands which toggle the states of the corresponding flip-flops. A relatively small number of addresses of the control RAM have change commands entered in correspondence with selected ones of the pins. By repeatedly reading out the commands in these addresses in a non-cyclic sequence it is possible to generate a succession of different states of the flip-flops in the logic, which succession is much longer than the number of addresses of the control RAM which are utilized. Apparatus for establishing the correct addressing sequence is described.

Abstract: A probe for sensing direction of flow of an injected current pulse along a conductor of a circuit under test is linked to an ATE, to be triggered to inject the pulse during a test sequence at a step previously found by the ATE to establish a faulty state in the circuit. Thus, the faulty one of several components connected to a circuit node can be identified. The probe itself can also be used independently, and injects an approximately triangular-waveform current pulse which has a steep rising edge and a less steep falling edge, thereby inducing a voltage pulse which is asymmetric about the zero voltage level and thus permits discrimination of the direction of current flow. The probe may have a single current injection contact disposed between the limbs of a bifurcated core for the pick-up coil.

Abstract: A probe for sensing direction of flow of an injected current pulse along a conductor of a circuit under test is linked to an ATE, to be triggered to inject the pulse during a test sequence at a step previously found by the ATE to establish a faulty state in the circuit. Thus, the faulty one of several components connected to a circuit node can be identified. The probe itself can also be used independently, and injects an approximately triangular-waveform current pulse which has a steep rising edge and a less steep falling edge, thereby inducing a voltage pulse which is asymmetric about the zero voltage level and thus permits discrimination of the direction of current flow. The probe may have a single current injection contact disposed between the limbs of a bifurcated core for the pick-up coil.

Abstract: A probe for sensing the direction of flow of an injected current pulse along a conductor of a circuit under test. The probe is linked to automatic test equipment (ATE), and is triggered to inject the pulse during a test sequence at a step previously found by the ATE to establish a faulty state in the circuit so that the faulty one of several components connected to a circuit node can be identified. The probe injects an approximately triangular-waveform current pulse which has a steep rising edge and a less steep falling edge, thereby inducing a voltage level and thus permits discrimination of the direction of current flow. To detect low level current pulses in the presence of masking noise, the output of the probe is connected to the series combination of a filter, an integrator and an A/D converter. The circuit under test is set to its faulty state, and then the probe is repeatedly operated, first with the injection of the current pulses inhibited and then with current pulses being injected.