B&B Electronics manual Appendix C RS-485 Connections, Serial Server DB-9 Pin-out in RS-485 Mode

RS-485 Connections RS-485 Connections

APPENDIX C: RS-485 CONNECTIONS

Serial Server DB-9 Pin-out in RS-485 Mode

RS-485		Direction	RS-485	DB9M
Signal Name				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

Note:

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.

Manual Documentation Number: ESP901-902_4105m Appendix C 79 80 Appendix D Manual Documentation Number: ESP901-902_4105m

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