New Developments in RS232 Interfaces
Design Note 4
Robert Dobkin
New RS232 interface chips have been developed that
offer significant advantages over older devices such
as the 1488 and 1489. The new RS232 interface ICs
improve speed, power, voltage supply requirements, and
protection over older devices. Further, the new chips
are easier to use, requiring fewer external components
and may be turned off to a “zero” power supply current
condition for use in battery powered systems.
The new RS232 drivers are implemented in a monolithic
bipolar technology. A unique output stage was designed
that provides large output swings, minimizing power
supply voltage requirements, while retaining outstanding overload protection features. The outputs can be
driven beyond the power supply voltage without drawing excessive current or forcing current back into the
power supplies. Of course, current limiting is included
to protect against short circuit conditions.
Initial consideration of technologies for implementing
RS232 interfacing might include CMOS as a possible
technology for this type of application. Power supply
requirements are low, output voltage swing is high,
and higher voltage CMOS technologies are available …