These devices consist of bus transceiver circuits, D-type flip-flops, and control circuitry arranged for multiplexed transmission of data directly from the input bus or from the internal registers. Data on the A or B bus is clocked into the registers on the low-to-high transition of the appropriate clock (CLKAB or CLKBA) input. Figure 1 illustrates the four fundamental bus-management functions that can be performed with the ´ABT646.
Output-enable () and direction-control (DIR) inputs are provided to control the transceiver functions. In the transceiver mode, data present at the high-impedance port may be stored in either register or in both.
The select-control (SAB and SBA) inputs can multiplex stored and real-time (transparent mode) data. The direction control (DIR) determines which bus will receive data when is low. In the isolation mode ( high), A data may be stored in one register and/or B data may be stored in the other register.
When an output function is disabled, the input function is still enabled and may be used to store and transmit data. Only one of the two buses, A or B, may be driven at a time.
To ensure the high-impedance state during power up or power down, should be tied to VCC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.
The SN74ABT646 is available in TI"s shrink small-outline package (DB), which provides the same I/O pin count and functionality of standard small-outline packages in less than half the printed-circuit-board area.
The SN54ABT646 is characterized for operation over the full military temperature range of -55°C to 125°C. The SN74ABT646 is characterized for operation from -40°C to 85°C.
