B&B Electronics ESP904 - Manual - Manual (Page 85)

RS-485 Connections
Manual Documentation Number: ESP904-4513m Appendix C 75
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 Park – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445 – www.bb-europe.com
A A P P P P E E N N D D I I X X C C : : R R S S - - 4 4 8 8 5 5 C C O O N N N N E E C C T T I I O O N N S S
ESP904 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 67. DB-9 Pin-out in RS-485 Mode
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.
Figure 68. 2-wire RS-485 Connection