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Serial Port Information
RS-232
© National Instruments Corporation
This appendix describes the RS-232, RS-422, and RS-485 standards and
explains some of the issues involved with these types of serial
communication.
Table D-1 lists the features of the RS-232, RS-422, and RS-485 standards.
Table D-1. RS-232, RS-422, and RS-485 Features
Feature
Type of
transmission lines
Maximum number
of drivers
Maximum number
of receivers
Maximum cable
length
Maximum data rate
Maximum CMV
Driver output
Driver load
As specified in the ANSI/EIA-232-D Standard, Interface Between Data
Terminal Equipment and Data Circuit-Terminating Equipment Employing
Serial Binary Data Interchange, RS-232 standardizes serial
communication between computers, and between computer terminals and
modems. Many applications use the RS-232 standard to interface
peripherals to personal computers. RS-232 uses transmission lines in which
the state of each signal is represented by referencing the voltage level of a
single line to ground. RS-232 was designed for serial communication up to
RS-232
Unbalanced
Differential
1
1
1
10
50 ft.
4,000 ft.
330 kbits/s
10 Mbits/s
± 25 V
±7 V
5 to 25 V
2 to 6 V
100 Ω
> 3 kΩ
D-1
ENET-232 and ENET-485 Series User Manual
D
RS-422
RS-485
Differential
32
32
4,000 ft.
10 Mbits/s
+12 to –7 V
1.5 to 6 V
60 Ω
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