These octal bus transceivers are designed for asynchronous two-way
communication between data buses. The control-function implementation
allows for maximum flexibility in timing.
These devices allow data transmission from the A bus to the B bus
or from the B bus to the A bus, depending upon the logic levels at
the output-enable (OEAB and )
The output-enable inputs disable the device so that the buses are
effectively isolated. The dual-enable configuration gives the
transceivers the capability to store data by simultaneously enabling
OEAB and . Each output
reinforces its input in this transceiver configuration. When both
OEAB and are enabled
and all other data sources to the two sets of bus lines are in the
high-impedance state, both sets of bus lines (16 total) remain at
their last states. The 8-bit codes appearing on the two sets of buses
are identical for the SN74ALS621A, SN74ALS623A, and SN74AS623 or
complementary for the SN74ALS620A.
The -1 versions of the SN74ALS620A and SN74ALS621A are identical
to the standard versions, except that the recommended maximum
IOL is increased to 48 mA in the -1 versions.
The SN74ALS620A, SN74ALS621A, SN74ALS623A, and SN74AS623 are
characterized for operation from 0°C to 70°C.