Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Patent
1998-12-29
2000-12-12
Karlsen, Ernest
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
324765, 714733, G01R 3128
Patent
active
061604135
ABSTRACT:
A test-mode latching circuit residing on an integrated circuit with test circuitry and operational circuitry has an enable state and a disable state. In the enable state, a test key is able to be latched so as to trigger a test mode. In the disable state, test key inputs are not latched, and thus, test modes are not entered. Initially, the circuit is readily enabled so that the IC can be tested upon fabrication. The circuit is locked in a disable state before external sale. A re-enable circuit is present to preclude inadvertent switching of the latching circuit back into the enable state during customer operation. Safeguards are implemented to avoid inadvertently re-enabling the latching circuit. To re-enable the latching circuit, an out-of-spec voltage is applied to an anti-fuse capacitor or programmable logic circuit while an out-of-spec voltage of the same or another signal is detected at a field device. In one embodiment, the state switches to the enable state in response to the out-of-spec voltage. In alternative embodiments, an additional or subsequent signal, such as a prescribed clock pattern, occurs before the first circuit switches to the enable state.
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Graalum Jason E.
Habersetzer Daryl L.
Kurth Casey R.
Mullarkey Patrick J.
Britt Trask
Karlsen Ernest
Micro)n Technology, Inc.
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