Section 7 Communication (Modbus)
7-2
Communication
(Modbus)
7.1 Communication method
■ Modbus communication protocol
The communication function is
used by creating a program on
the host computer. As such,
the explanations in this section
are from the perspective of the
host computer.
For example, "Read/Write"
refers to the host computer
reading or writing to the E5AR/
ER.
This communication method is based on RTU Mode of the Modbus
Protocol of Modicon Inc. (Specifications: PI-MBUS-300 Rev.J)
Detailed specifications for the Modbus protocol are shown below.
■ Communication specifications
* Initial settings are shaded.
■ Transfer protocol (Communication/Modbus)
The host computer sends a command frame, and the E5AR/ER sends
a response frame based on the content of the command frame. One
response frame is sent in response to one command frame.
The exchange between the command frame and response frame is
explained below.
After a receiving a response from the controller, have the host
computer wait at least 5 ms before sending the next command.
Supplement
Transfer connection: Multi-point
Communication method: RS-485 (2-wire half duplex)
Synchronization method: Start-stop
Communication speed: 9.6 k/19.2 k/38.4 k bit/s
Send code: RTU (Remote Terminal Unit)
Data length: 8 bits
Stop bit length: Automatically set by vertical parity setting
Error detection: Vertical parity None/Even/Odd
CRC-16 (Cyclical Redundancy Check)
Flow control: None
Interface: RS-485
Retry function: None
Response
frame
Command
frame
Response
frame
Command
frame
Host computer
E5AR/ER
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