The checkpoints of a circuit are all the wires in a network which are either primary input wires (external signals) or fan-out branches.
Fan-Out Branches
A fan-out point is a point in a network where a multiple path commences.
A fan-out stem refers to the wire preceding a fan-out point.
A fan-out branch refers to the wires just beyond the fan-out point.
In a combinatorial circuit, any test which detects all single stuck faults on all checkpoints detects all single faults in the circuit.
For example, consider faults at 2, 4 and 5 in the circuit below:
A fault at 2 will appear in a check for a fault at 4 and 5. Therefore, we do not need to consider faults at 2.
Summary bq
The checkpoints are the wires which are essential to test in order that we detect every possible fault.
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