16-bit bus transceiver/register; 3-state

The 74ALVCH16646 consists of 16 non-inverting bus transceiver circuits with 3-state outputs, D-type flip-flops and control circuitry arranged for multiplexed transmission of data directly from the internal registers. Data on the ‘A’ or ‘B’ bus will be clocked in the internal registers, as the appropriate clock (nCPAB or nCPBA) goes to a HIGH logic level. Output enable (nOE) and direction (nDIR) inputs are provided to control the transceiver function. In the transceiver mode, data present at the high-impedance port may be stored in either the ‘A’ or ‘B’ register, or in both. The select source inputs (nSAB and nSBA) can multiplex stored and real-time (transparent mode) data. The direction (nDIR) input determines which bus will receive data when nOE is active (LOW). In the isolation mode (nOE = HIGH), ‘A’ data may be stored in the ‘B’ register and/or ‘B’ data may be stored in the ‘A’ 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, nOE should be tied to VCC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking/current-sourcing capability of the driver.

Active bus-hold circuitry is provided to hold unused or floating data inputs at a valid logic level.