16-BIT BUS TRANSCEIVER AND REGISTER WITH 3-STATE OUTPUTS

This 16-bit Bus Transceiver and Register is designed for low-voltage (3.3-V) VCC operation. The SN74LVC16646 CAN be used as two 8-bit transceivers or one 16-bit transceiver. The device consists 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 SN74LVC16646. Output-enable (OE) and direction-control (DIR) inputs 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 circuitry used for select control eliminates the typical decoding glitch that occurs in a multiplexer during the transition between stored and real-time data. DIR determines which bus receives data when OE is low. In the isolation mode (OE 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 CAN 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, OE 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. Active bus-hold circuitry holds unused or floating data inputs at a valid Logic level. By Texas Instruments