Genrad, Inc.

Mark A Swanson

Aldo Mastrocola

An automated circuit board testing system, for performing in-circuit, functional or cluster tests, takes backdrive stress into account in selecting appropriate isolation methods for digital devices during the design of the test protocol. In other words, the design of the test includes an analysis of the circuit board and its components, and of the available methods to isolate the device- or function-under-test from the rest of the circuit board. The analysis includes a calculation of stress currents on upstream components resulting from backdriving, and a selection of methods from those available which will produce stress currents below a pre-selected level. In another aspect of the invention, the safe maximum run-time for the test using the available methods is computed.

Method and apparatus for circuit board testing with controlled backdrive

A technique for automatically diagnosing the failure of electronic devices connected to share a common bus. All bus devices are first disabled, and the bus is examined to determine if a failed device is interfering with normal operation by causing the bus to be stuck at a logic high or a logic low level. If the bus is stuck low or high, a forcing voltage nearly equal to either V.sub.ol or V.sub.oh, respectively, is applied to the bus, with all devices still disabled. A disabled bus current is then measured. One at a time, the bus devices are enabled, and the current on the bus measured to determine an enabled bus current. If, for a particular device, the enabled bus current exceeds the disabled bus current by a predetermined amount depending on the drive current specification of the device, it is concluded that the particular device is operating properly.

Method and apparatus for identifying defective bus devices

This disclosure is concerned with suppressing spurious signals generated during the in-circuit testing of circuit components, and which spurious signals may interfere with test signals being forced at selected nodes of the circuit that are inputs to components being tested and wherein such spurious signals may be routed via certain of the other circuit components, by automatically inhibiting either potential transmission of spurious signals by applying specific signals to components identified by analysis as normally feeding or processing input signals to the component(s) under test, or automatically inhibiting all inhibitable input parts of all components identified as those capable of passing such spurious signals to the input of the component(s) under test.

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Arlington, MA, United States of America

Mark A Swanson