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Using Modbus Communication
Serial communication can be performed with Direct Digital Controllers (DDCs) or similar devices using the Modbus protocol.
Modbus Communication Configuration
Modbus communication is configured using 1 master (PLC) and a maximum of 31 slaves. Serial communication between
master and slave is normally initiated by the master and responded to by the slaves.
The master performs serial communication with one slave at a time. Consequently, the slave address of each slave must be
initially set, so that the master can perform serial communication using that address. Slaves receiving commands from the
master perform the specified functions, and send a response back to the master.
Communication Specifications
The Modbus communication specifications are shown below:
Item
Interface
Communications Cycle
Communications Parameters
Communications Protocol
Number of Connectable Units
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Master
E7
Fig D.1 Example of Connections between Master and Drive
Table D.1 Modbus Communication Specifications
RS-422, RS-485
Asynchronous (Start-stop synchronization)
Baud rate:
Select from 1200, 2400, 4800, 9600, and 19200 bps.
Data length:
8 bits fixed
Parity:
Select from even, odd, or none.
Stop bits:
1 bit selected
Modbus
31 units max.
Communications D - 2
Slaves
E7
E7
Specifications
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