I/O pins connected to the communication bus. The test is based on sending and subsequently receiving a digital signal containing high and low levels. If the value received by the FMother from the FUT is identical to that sent, the IOB is functioning correctly. In order to attain this functionality, all that is required is to implement an entry/exit buffer at each of the bus pins (see Fig. 6a). In order to validate pin function in both directions, first a design with a buffer in one direction is downloaded, and then another design with a buffer in the other direction, thus providing information about correct entry/exit function.