MEsoftstart Modbus interfaces
The MEsoftstart PC App and any SCADA system, both use the same MODBUS protocol and either is the Modbus Master when
connected to the soft starter. The SCADA uses a subset of the total register definition. Some of the registers will only be used by
the PC Application (note: these register values will not be shown in the final SCADA SICD document).
The MEsoftstart Core variant supports only Modbus RTU using RS485 using connectors J1 and J2.
The MEsoftstart Pro variant supports two Modbus interfaces:
Modbus RTU on RS485 using connectors J2 and J3
Modbus TCP on Ethernet using connector J1 (Pro variants only)
Please request the Modbus Software Interface Control Document from your local distributor.
The following general guidelines apply:
The PC Application and the SCADA system may not be simultaneously present on the Modbus RTU RS-485 data bus due to
bus conflict issues. Two Modbus devices may be present – one on the Modbus TCP port and one on the Modbus RTU port.
The device that connects first, will be the Master and will be in control of the soft starter. The Master will be able to start,
stop and reset the soft starter. The other Modbus device will only be able to monitor the status and progress sent by the
The Modbus Master can to connect to the soft starter (via MODBUS messages) when the soft starter is in any state (Stopped,
Starting, Stopping or Running) and request status updates as well as read the soft starter's present configuration.
The soft starter configuration may only be updated by the Modbus Master when the soft starter is in the Stopped state. On
receipt of a new configuration, the soft starter checks the password and then performs a validity check on the received
parameters and responds either with errors, or with a positive response. A single configuration parameter compliance
failure, will result in the whole configuration will be discarded (refer paragraph 6.5).
The Modbus Master may send regular status request messages beginning when the soft starter is in Stopped mode. The
Modbus Master will then be in control of the soft starter and will remain in control, provided that a continuous regular
message is sent from the Master to the Soft starter. While the Modbus Master is in control of the soft starter the TFT display
will indicate this with the words "TCPCTL" or "RTUCTL", depending on if the TCP Modbus master is in control, or the RTU
If a second Modbus device is also present and monitoring, the TFT display will indicate "TCP" or "RTU" next to the control
indication – refer Figure 39.
If the soft starter does not receive messages from the Modbus Master for a period longer than 10 seconds, control will
revert to the other Modbus device present or to the soft starter TFT display if no other Modbus device is present. The
Modbus Master is required to ensure that it gets regular status updates from the soft starter at a recommended rate of
once per second to keep itself appraised of the most up-to-date status of the soft starter.
The soft starter is not able to distinguish when under Modbus control, whether it is the PC Application or a SCADA control
system that is the Modbus Master.
The soft starter Modbus interface does not support Modbus Broadcast mode or Silent mode.
The RS-485 RTU Modbus communication interface is default set to 115200 BAUD, 1 Start, 1 Stop, and Even Parity (with the
possibility of No Parity and Odd Parity available). This is reconfigurable from the Modbus Master and from the TFT display.
98 MEsoftstart PC Interface Application