RS422&RS485的通信规约介绍

RS-422/485 Application Note Cover Page

B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

PH (815) 433-5100 -- FAX (815) 434-7094

RS-422 and RS-485

Application Note

B&B Electronics Mfg. Co. Inc.

P.O. Box 1040 -- Ottawa, IL 61350

PH (815) 433-5100 -- FAX (815) 434-7094

RS-422/485 Application Note Table of Contents i

B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

PH (815) 433-5100 -- FAX (815) 434-7094

B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

RS-422/485 Application Note 1

B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

PH (815) 433-5100 -- FAX (815) 434-7094

an RS-422 and RS-485 system. This application note attempts to cover

enough technical details so that the system designer will have considered all

the important aspects in his data system design. Since both RS-422 and RS-

485 are data transmission systems that use balanced differential signals, it is

this application note the generic terms of RS-422 and RS-485 will be used to

represent the EIA/TIA-422 and EIA/TIA-485 Standards.

+3 to +12 and -3 to

-12 volts as shown in Figure 1.1.

Balanced Line Drivers

appears across a pair of signal lines that transmit only one signal. Figure 1.2

shows a schematic symbol for a balanced line driver and the voltages that

exist. A balanced line driver will produce a voltage from 2 to 6 volts across

its A and B output terminals and will have a signal ground (C) connection.

Although proper connection to the signal ground is important, it isn't used by

” condition of the driver.

The term “tristate” comes from the fact that there is a third output state of an

RS-485 driver, in addition to the output states of “1” and “0.”

B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

Figure 1.1

Figure 1.2