3. Notion of testability – Increasing testability

3.1 Key concepts

Testability can be broadly defined as the ability of a circuit or system to be tested. This aptitude depends on two complementary notions that are fundamental to testing:

• the controllability of each internal electrical node, i.e. the degree of ease with which each node can be forced to each logic level, by positioning suitable levels on the primary inputs of the circuit or system only;

• the observability of each internal electrical node, i.e. the degree of ease with which the logic level of each node can be determined simply by reading the primary outputs of the circuit or system.