Disclosed herein is a method of operating a system in a test mode. When the test mode is an ATPG test mode, the method includes beginning stuck-at testing by setting a scan control signal to a logic one, setting a transition mode signal to a logic 0, and initializing FIFO buffer for ATPG test mode. The FIFO buffer is initialized for ATPG test mode by setting a scan reset signal to a logic 0 to place a write data register and a read data register associated with the FIFO buffer into a reset state, enabling latches of the FIFO buffer using an external enable signal, removing the external enable signal to cause the latches to latch, and setting the scan reset signal to a logic 1 to release the write data register and the read data register from the reset state, while not clocking the write data register.