Appendix A Serial Port Information; Table A-1. Rs-232, Rs-422, And Rs-485 Features - National Instruments PCMCIA-232 Getting Started

Serial Port Information
RS-232
© National Instruments Corporation
This appendix discusses the RS-232, RS-422, and RS-485 standards
and explains some of the issues involved with these types of serial
communication.
Table A-1 lists the features of the RS-232, RS-422, and RS-485 standards.

Table A-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
RS-232, as specified in the ANSI/EIA-232-D Standard, Interface Between
Data Terminal Equipment and Data Circuit-Terminating Equipment
Employing Serial Binary Data Interchange, standardizes serial
communication between computers and between computer terminals and
modems. Most applications use the RS-232 standard for interfacing
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 RS-422
Single ended Differential
1 1
1 10
50 ft. 4,000 ft.
20 kbytes/s 10 Mbytes/s
±25 V ±7 V
5 to 25 V 2 to 6 V
100 Ω
>3 kΩ
A-1
A
RS-485
Differential
32
32
4,000 ft.
10 Mbytes/s
+12 to –7 V
1.5 to 6 V
60 Ω
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