Bidirectional Bus Transceivers in
High-Density 20-Pin Packages
Choice of True or Inverting Logic
A-Bus Outputs Are Open Collector;
B-Bus Outputs Are 3 State
Package Options Include Plastic
Small-Outline (DW) Packages and
Standard Plastic (N) 300-mil DIPs

description
These octal bus transceivers are designed for asynchronous two-way communication between open-collector
and 3-state buses. The devices transmit data from the A bus (open-collector) to the B bus (3 state) or from the
B bus to the A bus, depending on the logic level at the direction-control (DIR) input. The output-enable (OE) input
can be used to disable the device so the buses are isolated.
The -1 version of SN74ALS638A is identical to the standard version, except that the recommended maximum
IOL is increased to 48 mA.
The SN74ALS638A, SN74ALS639A, SN74AS638A, and SN74AS639 are characterized for operation from 0°C
to 70°C.