Remote Modbus Communications
7.16
Remote Modbus Communications
The MX
2
starter provides a Modbus RTU to support remote communication.
The communication interface is RS-485, and allows up to 247 slaves to be connected to one master (with repeaters when the number of
drops exceeds 31). Please refer to Figures 49 and 50 for connection diagrams.
7.16.1 Supported Commands
The MX
2
supports the following Modbus commands:
• Read Holding Registers (03 hex)
• Read Input Registers (04 hex)
• Preset Single Register (06 hex)
• Preset Multiple Registers (10 hex)
Up to 64 registers may be read or written with a single command.
7.16.2 Modbus Register Addresses
The Modbus specification defines holding registers to begin at 40001 and input registers to begin at 30001. Holding registers may be
read and written. Input registers may only be read.
In the MX
2
, the register maps are identical for both the holding registers and the input registers. For example, the Motor FLA parameter
is available both in holding register 40101 and in input register 30101. This is why the register addresses in the Modbus Register Map
are listed with both numbers (e.g. 30101/40101).
7.16.3 Cable Specifications
Good quality twisted, shielded communications cable should be used when connecting to the Modbus port on the MX
2
. The cable
should contain two twisted pairs and have an overall shield. Use one pair of conductors for the A(-) and B(+) signals. Use the other pair
of conductors for the Common signal. The cable should adhere to the following specifications.
• Conductors: 2 twisted pair
• Impedance: 100 Ohm to 120 Ohm
• Capacitance: 16 pF/ft or less
• Shield: Overall shield or individual pair shields
Examples of cables that meet these specifications are Belden part number 9842 and Alpha Wire part number 6412.
171
7 - THEORY OF OPERATION
Figure 49: TB4 Connector
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