Eaton SLX9000 - Table 5-15: Modbus Commands Supported by SLX9000

SLX9000 Adjustable Frequency Drives User Manual
MN04003020E
For more information visit: www.eaton.com 5-23
January 2009
Modbus RTU Protocol
Modbus RTU protocol is a simple but effective fieldbus protocol. Modbus network has a
bus topology, where every device has an individual address. With the help of the
individual bus addresses the commands are directed to the single devices within the
network. Modbus supports also broadcast-type messages, that are received by every
device of the bus. Broadcast messages are sent to the address “0” which is reserved for
these messages.
The protocol includes CRC error detection and parity check for preventing the handling
of messages containing errors. In Modbus the data is transferred in hex mode a
synchronically and a break of approximately 3.5 characters is used as an end character.
The length of the break depends on the used baud rate.
Table 5-15: Modbus Commands Supported by SLX9000
Termination Resistor
The RS-485 bus is terminated with 120Ω termination resistors in both ends. SLX9000 has a
built-in termination resistor which is switched off as a default. See the jumper selections in
Chapter 4.
Modbus Address Area
The Modbus bus of SLX9000 uses the ID numbers of the application as addresses. The ID
numbers can be found in the parameter tables of the application manual.
When several parameters/monitoring values are read at a time they must be consecutive.
11 addresses can be read and the addresses can be parameters or monitoring values.
Modbus Process Data
Process data is an address area for fieldbus control. Fieldbus control is active when the value
of parameter 3.1 (Control place) is 2 (= fieldbus). The contents of the process data has been
determined in the application. The following tables present the process data contents in the
Multi-Control Application.
Function
Code Function Name Address
Broadcast
Messages
03 Read Holding Register All ID numbers No
04 Read Input Register All ID numbers No
06 Preset Single Register All ID numbers Yes
16 Preset Multiple Register All ID numbers Yes