12-bit to 24-bit multiplexed bus exchanger with 3-state outputs

This 12-bit to 24-bit bus exchanger is designed for 1.65-V to 3.6-V VCC operation.

The SN74ALVCH16271 is intended for applications in which two separate data paths must be multiplexed onto, or demultiplexed from, a single data path. This device is particularly suitable as an interface between conventional DRAMs and high-speed microprocessors.

A data is stored in the internal A-to-B registers on the low-to-high transition of the clock (CLK) input, provided that the clock-enable (CLKENA\) inputs are low. Proper control of these inputs allows two sequential 12-bit words to be presented as a 24-bit word on the B port.

Transparent latches in the B-to-A path allow asynchronous operation to maximize memory access throughput. These latches transfer data when the latch-enable (LE\) inputs are low. The select (SEL\) line selects 1B or 2B data for the A outputs. Data flow is controlled by the active-low output enables (OEA\, OEB\).

To ensure the high-impedance state during power up or power down, the output enables 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 undriven inputs at a valid logic state. Use of pullup or pulldown resistors with the bus-hold circuitry is not recommended.