The registers in the DM74ALS646 are edge-triggered Dtype flip-flops. On the positive transition of the clock (CAB or CBA), the input bus data is stored into the appropriate register. The CAB input controls the transfer of data into the A register and the CBA input controls the B register. The SAB and SBA control pins are provided to select whether real-time data or stored data is transferred. A LOW input level selects real-time data, and a HIGH level selects stored data. The select controls have a "make before break" configuration to eliminate a glitch which would normally occur in a typical multiplexer during the transition between store and real-time data. The enable G and direction control pins provide four modes of operation: real-time data transfer from bus A to B, realtime data transfer from bus B to A, real-time bus A and/or B data transfer to internal storage, or internally stored data transfer to bus A or B.