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RS-485 Connections
Manual Documentation Number: ESP901-902_0508m Appendix C 79
B&B Electronics Mfg Co Inc – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com
B&B Electronics Ltd – Westlink Commercial Pk – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
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Serial Server DB-9 Pin-out in RS-485 Mode
RS-485
Signal Name
Direction RS-485 DB9M
Pin
Data B (+) In/Out DATA B (+) 3
Data A (−) In/Out DATA A (−) 4
Signal Ground --- GND 5
Figure 70. DB-9 Pin-out in RS-485 Mode
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Some RS-485 devices are marked opposite the RS-485 standard,
which defines the Data B line as positive relative to Data A during a
Mark state before enabling the transmitter, and after transmitting
before tri-stating. If an RS-485 device does not respond, try swapping
the Data B and Data A lines.
Figure 71. 2-wire RS-485 Connection
To connect 4-Wire RS-485 devices, the RS-422 Mode can be used
provided the
Serial Server will be connected as a master in a single
master system. If using multiple masters, the Serial Server cannot be
used, as it does not tri-state the transmitter in RS-422 mode.