A SCAN TEST SYSTEM AND METHOD FOR MANIPULATING LOGIC VALUES THAT REMAIN CONSTANT DURING NORMAL OPERATIONS

摘要

The present invention is a system and method that holds a logic value constant during normal operations and facilitates manipulation of the logic value during scan test operations. In one embodiment the present invention is a constant logic value manipulation scan test chain that includes a combinational circuit, a constant logic value scan test manipulation circuit, and a scan test element. The a combinational circuit performs functional operations during normal mode. The constant logic value scan test manipulation circuit provides a logic value output that remains constant during normal operations and changes in accordance with scan test input information during scan test operations. The scan test element communicates test vectors to functional components and interacts with functional logic utilized to perform normal operations. In one exemplary implementation of the present invention the combinational circuit is a logic gate and the logic value output by the constant logic value scan test manipulation circuit is coupled to an input of the logic gate. The logic value input to the logic gate remains constant during normal operations and is manipulated in accordance with scan test input information during scan test operations.