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As opposed to extended interconnect testing, which refers to measurements in passive components interconnecting analog pins, simple interconnect testing addresses the detection of the usual structural defects, such as short and open circuits. It is important to refer that simple interconnect testing is entirely digital, in the sense that fault detection is carried out by shifting (in / out) test vectors / responses.

The basic principle underlying the detection of short-circuits among analog pins may be presented as shown in figure 1. Such as for digital pins, the detection procedure consists of applying complementary “logic values” (V_H, V_L) to the interconnects under test.

Figure 1: Short-circuit detection among analog pins.

By recalling the switching structure of the ABMs, it becomes clear that the application of V_H and V_L voltages can be accomplished by closing switches S_H and S_L (e.g. by shifting appropriate 4-bit words into the ABM control structure section of the BS register). The comparators present in this switching structure will then convert the voltage levels at the analog inputs into a digital value, which is read at the first stage of the same 4-bit ABM control structure. The whole process is therefore carried out by shifting in / out through the BS register, and the ATAP pins do not play any role in the simple interconnect test procedures.

Figure 2: Switching structure configuration for simple interconnect testing.