[previous] [next] [contents]    Interconnect testing with 1149.4

The detection of open or short-circuit faults with 1149.4 is similar as with 1149.1 and may be summarised as follows:

• In the case of digital pins, the data is loaded directly into the DBMs
• In the case of analog pins, the control codes that cause internally generated voltages (V_H or V_L) to be applied to the pins are loaded into the ABMs
• Test vector application and response capturing starts with the SAMPLE / PRELOAD instruction to shift in the first test vector and deals only with digital data (both for digital and analog pins)

It is particularly important to emphasise the fact that interconnect testing uses only digital test vectors, even for analog pins, and is based exactly in the same algorithms used for digital-only circuits, since:

• The high (V_H) and low (V_L) voltages applied to analog function pins are generated internally
• V_H or V_L are applied to the analog output pins as defined by the data shifted into the control structure of the ABMs
• The responses present at each analog input pin are converted to digital through the comparator present in the switching structure of the ABMs and read into the DATA bit in the capture / shift stage of the ABMs control structure

Notice also that interconnect testing does not use the ATAP pins, which are only necessary when analog signals are to be applied or captured (and namely in parametric testing), as will be shown in the following section.