Introduction to MODBUS

The CTM-ONE and CTM-500 support 4 types of MODBUS:

MODBUS Master Gateway
MODBUS Slave Gateway
- TCP Slave
- Serial Slave
- Self-Slave

The mode setting of the serial port must be set to MODBUS for the RS232/RS485 port setting for MODBUS configuration to work even if no physical RS232 or RS485 devices are physically connected to the CTM device.

MODBUS configuration is available on the CTM local web interface under serial < modbus tab.

The RS232 and RS485 tabs expand for specific MODBUS functionality. The CTM supports simultaneous RS232 and RS485 protocols so individual configurations can exist for either protocol.

For Ethernet-based MODBUS communication (TCP / RTU over UDP), either MODBUS RS232 or RS485 can be used.

The “Mode” defines the Gateway Master or Gateway Slave operating state.

Access must also be enabled for routing data via the wireless network when using MODBUS. This can be found under Configuration > Firewall > Service Access Rules.

Make sure that field “Enable this rule” is checked off.