TransPort Modbus Configuration

Overview
 
This section will walk through settings for configuring the Modbus engine on the serial port for both Master and Slave configurations.  For sending Modbus data from the TransPort’s Cellular interface to an Ethernet interface (i.e. – Incoming Modbus/TCP over Cellular), please refer to:  HOW TO: Configure Port Forwarding with Digi TransPort Routers.
 
Assumptions
 
This guide assumes that the serial port that will be used is pre-configured with the correct baud rate, data bits, stop bits, etc that will be needed to talk to the end Modbus serial device.  This guide will not cover all of the Modbus settings, only those that are needed for basic configurations – refer to the Digi TransPort User Guide or more information on items not covered here.

NOTE:  Depending if the TransPort will be the Master or the Slave, you should follow the appropriate (Master or Slave) instructions below.  For example, if you have a SCADA Server that polls a meter, the TransPort should be the Master.  Otherwise, if the meter initiates traffic to the SCADA Server, then the TransPort should be the Slave.
 
Modbus Master Configuration
 
1) Log into the WebUI, and navigate to Configuration – Network > Legacy Protocols > MODBUS Gateway > MODBUS x, as shown in the screenshot below (this example will use MODBUS 0).
2) Check the box for Enable MODBUS Gateway to enable the feature.
3) Select the Async Port to use as the Modbus port.  The built-in serial port of all TransPort’s will be 0, and if an expansion card is installed (WR41/44 only), the additional serial ports will be 1-3.
4) Select the Async Mode to use, which is either RS232 or RS485.
5) Select the Duplex Mode to use, which is either full or half.
6) Select act-as-master for the Operation Mode setting.
7) Set the Idle Gap for the Modbus messages. This example uses 20 ms.
8) Choose the IP Port that will be needed for the Modbus communication.  The default Modbus port is 502.
9) Choose the Number of Sockets that can connect to the port.
10) Select the IP Mode for the connection, which is either TCP or UDP.
11) Click the Apply button and Save the changes.
 
Modbus Slave Configuration
 
1) Log into the WebUI, and navigate to Configuration – Network > Legacy Protocols > MODBUS Gateway > MODBUS x (this example will use MODBUS 0).
2) Check the box for Enable MODBUS Gateway to enable the feature.
3) Select the Async Port to use as the Modbus port.  The built-in serial port of all TransPort’s will be 0, and if an expansion card is installed (WR41/44 only), the additional serial ports will be 1-3.
4) Select the Async Mode to use, which is either RS232 or RS485.
5) Select the Duplex Mode to use, which is either full or half.
6) Select act-as-slave for the Operation Mode setting.
7) Set the Slave response value for a timeout that works for the setup.  This example uses 2 seconds.
8) Click the Apply button to apply the changes.
9) Navigate to Configuration – Network > Legacy Protocols > MODBUS Gateway > MODBUS Slaves.
10) Fill in the Slave addresses/unit ids field with the Modbus ID that is needed.
11) Fill in the Remote Host of the Modbus Master that will receive the connection.
12) Fill in the IP Port that the Modbus Master will use (the Modbus/TCP default is 502).
13) Select the IP Mode that will be used, which is either TCP or UDP.
14) Click the Add button to add the settings to the table.
15) Click the Apply button and Save the changes.