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2-11- MODBUS RTU
2- 11.1 General notes
The purpose of this document is to give the instructions to communicate with the Genset with a Modbus Master device, through the Modbus RTU
(zero-based) serial protocol.
The Genset controller can be configured as a Modbus slave device, that can be queried by a Modbus master device. The Modbus communication
anyway must be established and configured by skilled users following the Modbus protocol rules. For more documentation about the Modbus
protocol, please refer to the following link:
http://www.modbus.org/specs.php
For first tests and trials it’s possible to use the demo version of the Modbus Poll program, downloadable at the following link:
http://www.modbustools.com/modbus_poll.asp
The Genset has 2 ports that can be used for the Modbus communication: 1 RS232 and 1 RS485.
2- 11.2 Genset Controller configuration
The only thing to configure in the Genset is the serial port. Go to Connectivity setup M7, then select Serial setup M7.1.
If you are using the RS485 port, check that parameter B is set to
Modbus Slave
. Then set parameter C to the desired speed of communication,
and parameter A that is the address of the device. If you are using more than one device, be sure that all of them have a di
ff
erent address.
If you are using the RS232 port, check that parameter E is set to
Modbus Slave
. Then set parameter F to the desired speed of communication, and
parameter A that is the address of the device.
2- 11.3 Modbus command available
It’s possible to send 2 different types of requests to the Genset. A reading requests or read single registers (modbus function: 03) or a writing
request to set a single register (modbus function: 06). Every register is composed by 1 word (2 bytes).
The function 03-Read Holding Registers permits to read one or more registers from the Genset.
Example:
Request: Send to slave address 25 the request of reading register 69:
Answer:
The function 06-Preset Single Register permits to set one register of the Genset to a desired value.
Example:
Request: Send to slave address 35 the request of writing the value 928 into register 26:
Slave
address
Function
Address of the desired
register
Number of registers
required
CRC checksum
Slave
address
Function
CRC checksum
Number of
bytes
Value of the required
register
Slave
address
Function
Address of the desired
register
Value to set in the
register
CRC checksum
