SN74HC646

The 'HC646 consist of bus-transceiver circuits with 3-state outputs, 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 busmanagement functions that can be performed with the 'HC646.

Output-enable (OE) and direction-control (DIR) inputs SN74HC646 control the transceiver functions. In the transceiver mode, data present at the high-impedance port may be stored in either or both registers.

The select-control (SAB and SBA) inputs SN74HC646 can multiplex stored and real-time (transparent mode) data. DIR determines which bus receives data when OE is active (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 SN74HC646 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.

The SN54HC646 is characterized for operation over the full military temperature range of 55°C to 125°C. The SN74HC646 is characterized for operation from 40°C to 85°C.