You can attach the SmartServer IoT to one RS-485 network to communicate with Modbus RTU devices. You can also create your own RS-485 driver for the SmartServer IoT to communicate with RS-485 devices using protocols other than Modbus.

Note: Modbus can only be configured on one RS-485 port (default is port 1).

The SmartServer IoT includes two isolated RS-485 multi-drop bus ports. The two ports are available on two removable green 4-pin connectors as shown in the following figure, with the two interfaces labelled as RS-485 1 and RS-485 2

The screw terminals on the RS-485 plugs accept 0.22mm – 3.3mm (22 – 12AWG) gauge solid wire. The optimum tightening torque for the screw terminals is 0.75 Newton-meters  (6 lbs. in.) maximum. The ideal flathead screwdriver tip width for use with the screw terminal connectors is 3mm (0.12”). Strip wires to a length of 7mm (0.28”). You can use an insulated cord pin end to prevent fraying and inadvertent contact with adjacent terminals.  



The following table describes the two RS-485 connectors. 

Label

Name                        

Description

RT+

+ Receive/Transmit

The RS-485 positive receive/transmit connectors are labelled RT+.  These connections are polarity-sensitive, and must not be reversed.  Reversing polarity will cause improper bus operation. 

RT-

- Receive/Transmit

The RS-485 negative receive/transmit connectors are labelled RT-.  These connections are polarity-sensitive, and must not be reversed.  Reversing polarity will cause improper bus operation. 

SCSignal Common

The signal common (SC) pin provides a common signal reference ground.  You can connect this pin to the shield of a shielded cable to improve noise immunity. You can connect the signal common to earth ground on no more than one device on an RS-485 channel. To connect SC to earth ground at the SmartServer IoT, insert a jumper connecting SC to the earth ground pin to the left of the SC pin, and also connect the earth ground connector on the SmartServer IoT power input to earth ground.

   

Earth GroundYou can connect the signal common (SC) pin to earth ground on no more than one device on an RS-485 channel.