74F646, 74F646A Octal transceiver/register, non-inverting (3-State)
74F648, 74F648AOctal transceiver/register, inverting (3-State)

The 74F646/74F646A and 74F648/74F648A transceivers/registers
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 the internal registers. Data on
the A or B bus will be clocked into the registers as the appropriate
clock pin goes high. Output enable (OE) and DIR pins 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 both.
The select (SAB, SBA) pins determine whether data is stored or
transferred through the device in real–time. The DIR determines
which bus will receive data when the OE is active low. In the
isolation mode (OE = high), data from bus A may be stored in the B
register and/or data from bus B may be stored in the A register.
When an output function 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.