Abstract: A method and circuitry allows for the prevention of tester induced failures and reliability problems which occur when a tester creates bus contention by overdriving output pins of an integrated circuit. For each input/output (I/O) pad which is used for the output of data, a first signal on an output data line is compared with a second signal which is currently on the I/O pad. When the output is enabled and the comparison indicates the first signal is not equal to the second signal, the I/O pad is isolated from the output data line. The I/O pad is isolated, and thus in shutdown mode, until the I/O pad is no longer being driven to a signal value which is different than the signal value of the first signal on the output data line. Further, each I/O pad may be electrically isolated from its output data line whenever a comparison for any I/O pad indicates that the signal for the I/O pad is not equal to the signal on its output data line.