The 'ALVTH16821 devices are 20-bit bus-interface flip-flops with 3-state outputs designed for 2.5-V or 3.3-V VCC operation, but with the capability to provide a TTL interface to a 5-V system environment.
The devices can be used as two 10-bit flip-flops or one 20-bit flip-flop. The 20-bit flip-flops are edge-triggered D-type flip-flops. On the positive transition of the clock (CLK), the flip-flops store the logic levels set up at the D inputs.
A buffered output-enable (OE\) input can be used to place the ten outputs in either a normal logic state (high or low level) or a high-impedance state. In the high-impedance state, the outputs neither load nor drive the bus lines significantly. The high-impedance state and increased drive provide the capability to drive bus lines without need for interface or pullup components.
OE\ does not affect the internal operation of the flip-flops. Old data can be retained or new data can be entered while the outputs are in the high-impedance state.
When VCC is between 0 and 1.2 V, the device is in the high-impedance state during power up or power down. However, to ensure the high-impedance state above 1.2 V, 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 is provided to hold unused or floating data inputs at a valid logic level.
The SN54ALVTH16821 is characterized for operation over the full military temperature range of -55°C to 125°C. The SN74ALVTH16821 is characterized for operation from -40°C to 85°C.
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