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零件编号 | RS-422 | ||
描述 | RS-422 / RS-485 | ||
制造商 | B & B | ||
LOGO | |||
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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
Internet Addresses:
B&B Home Page:
http://www.bb-elec.com
Customer Service:
Technical Support:
© B&B Electronics - Revised October 1997
RS-422/485 Application Note
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
Cover Page
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Figure 1.5
RS-422/485 Application Note
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
5
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Chapter 2: System Configuration
Network Topologies
Network configuration isn’t defined in the RS-422 or RS-485 specification.
In most cases the designer can use a configuration that best fits the physical
requirements of the system.
Two Wire or Four Wire Systems
RS-422 systems require a dedicated pair of wires for each signal, a
transmit pair, a receive pair and an additional pair for each
handshake/control signal used (if required). The tristate capabilities of RS-
485 allow a single pair of wires to share transmit and receive signals for half-
duplex communications. This “two wire” configuration (note that an
additional ground conductor should be used) reduces cabling cost. RS-485
devices may be internally or externally configured for two wire systems.
Internally configured RS-485 devices simply provide A and B connections
(sometimes labeled “-“ and “+”).
Devices configured for four wire communications bring out A and B
connections for both the transmit and the receive pairs. The user can connect
the transmit lines to the receive lines to create a two wire configuration. The
latter type device provides the system designer with the most configuration
flexibility. Note that the signal ground line should also be connected in the
system. This connection is necessary to keep the Vcm common mode voltage
at the receiver within a safe range. The interface circuit may operate without
the signal ground connection, but may sacrifice reliability and noise
immunity. Figures 2.1 and 2.2 illustrate connections of two and four wire
systems.
RS-422/485 Application Note
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
13
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页数 | 30 页 | ||
下载 | [ RS-422.PDF 数据手册 ] |
零件编号 | 描述 | 制造商 |
RS-422 | RS-422 / RS-485 | B & B |
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