Modbus Communications Configuration; Transmission Modes; Message Structure For Rtu Mode; Address - Fairford agility Series User Manual

Communication (continued)

Modbus Communications Configuration

The Modbus communication settings may be configured from the Device menu:
Device >> Networks >> Modbus Network Settings >> Address (1 – 32)
•
Device >> Networks >> Modbus Network Settings >> Baud (9600 – 115200)
•
Device >> Networks >> Modbus Network Settings >> Parity (Odd / Even)
•
(Data bits = 8, Stop bits = 1)
•
The communication parameters should be set before connecting the Modbus master.

Transmission Modes

ASCII and RTU transmission modes are defined in the Modbus protocol specification. agility
RTU mode for the message transmission.

Message Structure For RTU Mode

The Modbus RTU structure uses a master-slave system for message exchange. In the case of the
agility system, it allows up to 32 slaves, and one master. Every message begins with the master
TM
making a request to a slave, which responds to the master in a defined structure. In both messages
(request and answer), the used structure is the same:
Address, Function Code, Data and CRC.
•
Master (request message):
Slave (response message):

Address

The master initiates the communication by sending a byte with the address of the destination slave.
When responding, the slave also initiates the message with its own address. Broadcast to address 0
(zero) is not supported.

Function Code

This field contains a single byte, where the master specifies the type of service or function requested to
the slave (reading, writing, etc.). According to the protocol, each function is used to access a specific type
of data.

Data Field

The format and contents of this field depend on the function used and the transmitted value.
agility TM Series Soft Start User Manual
MAN-AGY-001. Version 04. 21/09/2018
Address Function
(1 byte) (1 byte)
Address Function
(1 byte) (1 byte)
40
TM
Request Data (n CRC
bytes)
(2 bytes)
Response Data
CRC
(n bytes) (2 bytes)
uses only the