B&B Electronics ESR901 User Manual
Page 85
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.