74HC646

The 74HC646 is high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard no. 7A.

The 74HC646 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 internal registers. Data on the "A" or "B" bus will be clocked into the registers as the appropriate clock (CP_AB and CP_BA) goes to a HIGH logic level. Output enable (OE) and direction (DIR) 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 (S_AB and S_BA) of the 74HC646 can multiplex stored and real-time (transparent mode) data. The direction (DIR) input determines which bus will receive data when OE is active (LOW). In the isolation mode (OE = 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 of the 74HC646 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.

The "646" is functionally identical to the "648", but has non-inverting data paths.