In this example, Geo SCADA Expert is configured to use Modbus RTU (the Modbus serial protocol) to communicate with a Modbus Slave device that is connected serially to a terminal server.
The Modbus Slave device is connected to Geo SCADA Expert via a remote serial port, rather than directly to the local Geo SCADA Expert computer. The terminal server is connected to Geo SCADA Expert via an Ethernet link.
Example:
A Simple Modbus Scanner is to scan addresses 30001 to 30010 inclusive on a Slave device’s Input registers.
Within Geo SCADA Expert, a Simple Modbus Channel is configured as follows:
Primary Port Connection Type: TCP/IP
Within Geo SCADA Expert, a Simple Modbus Scanner is configured as follows:
On the Scanner tab of the Modbus Scanner Form:
Channel: Configured to reference the Modbus Channel indicated above
Device Address: Configured with the Modbus Slave’s address number
Data Address: 1 (the start of the scan block is 30000 + 1 = 30001)
Data Length: 9 (the end of the scan block is 30000 + 1 + 9 = 30010)
Location: Input Registers (the scanner scans registers in the 30000 address range)
On the Primary Port tab of the Modbus Scanner Form:
Connection Type: Network
Host Address: Configured with the IP address of the terminal server
Port: Configured with the identifier of the TCP port at the terminal server that is used for the Modbus serial communications port. (The Port number is not the serial communications port number.)
Communications Type: Modbus RTU (as the Simple Modbus driver uses the Modbus serial protocol, but communicates initially via an Ethernet communications link). (If the driver was using direct Ethernet communications to talk to a Modbus PLC, the Communications Type would be configured as Modbus TCP.)
Simple Modbus points are configured as required (see earlier in this section for Configuration Examples).