Network
Communications
6
6.2 Modbus Communications
SIEPYEUOQ2A01A AC Drive Q2A Technical Manual 215
6.2 Modbus Communications
This section gives detailed information about the parameters, error codes and communication procedures for
Modbus communications.
◆ Configure Master/Slave
You can use the Modbus protocol for serial communication with programmable controllers (PLC).
The Modbus communication uses one master (PLC) and a maximum of 31 slave drives. Serial communications
usually starts with a signal from the master to the slave drives.
A slave drive that receives a command from the master does the specified function and then sends a response back
to the master. You must set the address number for each slave drive before you start signal communications to
make sure that the master uses the correct address numbers.
A - Master (PLC) B - Slave (drive)
Figure 6.1 PLC and Drive Connection Example
◆ Communication Specifications
Table 6.2 Modbus Specifications
Item Specification
Interface RS-485
Synchronization method Asynchronous (start-stop synchronization)
Communication parameter
Communications speed: 1.2, 2.4, 4.8, 9.6, 19.2, 38.4, 57.6, 76.8, 115.2 kbps
Data length: 8 bit (fixed)
Parity: even, odd, none
Stop bit 1 bit (fixed)
Communication protocol Modbus standard (RTU mode only)
Number of possible units to connect Maximum: 31 units
◆ Communication with the PLC
This section gives information about the settings for the termination resistor and how to connect to Modbus
communications. Modbus communications uses an RS-485 interface (2-wire sequence).
■ Connect Communications Cable
Use this procedure to start communication between the PLC and drive.
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