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RS-485 Connections
Manual Documentation Number: ESR90x-0508m Appendix C 75
B&B Electronics Mfg Co Inc – 707 Dayton Rd - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104 – www.bb-elec.com
B&B Electronics Ltd – Westlink Commercial Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
ESR90x DB-9 Pin-out in RS-485F (four-wire, full duplex) Mode
RS-422
Signal Name
Direction
RS-422
DB9M
Pin
Receive Data A (−) In RXDA (−) 1
Receive Data B (+) In RXDB (+) 2
Transmit Data B (+) Out TXDB (+) 3
Transmit Data A (−) Out TXDA (−) 4
Signal Ground --- GND 5
Clear to Send A (−) In CTSA (−) 6
Clear to Send B (+) In CTSB (+) 7
Request to Send B (+) Out RTSB (+) 8
Request to Send A (−) Out RTSA (−) 9
Figure 54. RS-422 Connections in a DB-9 Connector
N
N
o
o
t
t
e
e
:
:
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.