Fault coverage for G-logic shall include only faults detected by hard detections. Potential detections shall not be considered directly in calculating the fault coverage. No number of potential detections of a fault shall imply that the fault would be detected.
Some potential detections can be converted into hard detections for the purpose of calculating fault coverage. If it can be shown that a fault is only potentially detected by fault simulation but is in fact detectable by the ATE by a difference not involving an X value, then upon documenting those conditions in the fault simulation report that fault shall be considered to be detected as a hard detection and the fault coverage shall be adjusted accordingly.
Faults associated with three-state buffer enable signal lines can cause X states to occur on nodes with fan-in branches, or erroneous Z states to occur on three-state primary outputs that may be untestable on some ATE. These faults may then be detectable only as potential detections, but may be unconvertible into hard detections. In such cases, it is permissible for the fault simulation report to state separately the fraction of the undetected faults that are due to