Impedance measurements require the use of the ATAP pins, together with the TBIC and ABMs, to apply and read analog test stimulae. The measurement of an impedance between a pin and ground may be done using the set up shown in figure 1.
Figure 1: Test set up for measuring an impedance between pin and ground.
The measurement procedure may be summarised as follows for this case:
Notice that the error margin in this procedure depends on the relative values of the unknown impedance (ZD), the voltmeter input impedance (ZV) and the impedance of each switch in the measurement path. The value obtained for ZD will only be acceptable if the following assumptions are valid:
ZV + ZS6 + ZSB2 >> ZD (to guarantee that the percentage of IT which does not flow through ZD is negligible)