These 18-bit universal bus transceivers combine D-type latches and D-type flip-flops to allow data flow in transparent, latched, and clocked modes. Data flow in each direction is controlled by output-enable (OEAB and OEBA\), latch-enable (LEAB and LEBA), and clock (CLKAB\ and CLKBA\) inputs.
For A-to-B data flow, the device operates in the transparent mode when LEAB is high. When LEAB is low, the A data is latched if CLKAB\ is held at a high or low logic level. If LEAB is low, the A data is stored in the latch/flip-flop on the high-to-low transition of CLKAB\. Output-enable OEAB is active high. When OEAB is high, the outputs are active. When OEAB is low, the outputs are in the high-impedance state.
Data flow for B to A is similar to that of A to B but uses OEBA\, LEBA, and CLKBA\. The output enables are complementary (OEAB is active high and OEBA\ is active low).
The B-port outputs, which are designed to source or sink up to 12 mA, include equivalent 25- series resistors to reduce overshoot and undershoot.
When VCC is between 0 and 2.1 V, the device is in the high-impedance state during power up or power down. However, to ensure the high-impedance state above 2.1 V, OE\ should be tied to VCC through a pullup resistor and OE should be tied to GND through a pulldown resistor; the minimum value of the resistor is determined by the current-sinking/current-sourcing capability of the driver.
The SN54ABT162500 is characterized for operation over the full military temperature range of -55°C to 125°C. The SN74ABT162500 is characterized for operation from -40°C to 85°C.
A-to-B data flow is shown: B-to-A flow is similar but uses OEBA\, LEBA, and CLKBA\.
Output level before the indicated steady-state input conditions were established
§ Output level before the indicated steady-state input conditions were established, provided that CLKAB\ was low before LEAB went low