According to one embodiment, a method of conducting a switching state (AC) loop back test at a buffer circuit comprises varying the relationship between the generation of strobe signals at a strobe input/output (I/O) circuit of a first group of I/O circuits and the reception of data at the first group of I/O circuits receiving the strobe signals fails, and comparing the time at which the first I/O circuit fails with a predetermined timing performance for the first group of I/O circuits. Subsequently, it is determined whether the first group of I/O circuits satisfies the predetermined timing performance.