74F647/74F649 pdf datasheet (O

74F647 Octal transceiver/register, non-inverting (open-collector)
74F649 Octal transceiver/register, inverting (open-collector)

The 74F647 and 74F649 Transceivers/Registers consist of bus
transceiver circuits with open-collector 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 will be clocked into the registers as the appropriate clock
pin goes to a High logic level. 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) controls can multiplex stored and real-time
(transparent mode) data. The DIR determines which bus will receivedata when the Output Enable, OE is active Low. In the isolation
mode (Output Enable, 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. The following
examples demonstrate the four fundamental bus-management
functions that can be performed with the 74F647 and 74F649.