Automation Direct Stellar SR55 Series User Manual

Page 5–4 Stellar
®
SR55 Series Soft Starter User Manual – 1st Ed, Rev F – 09/18/2019
Chapter 5: Communications
modbus serial CommuniCaTions (ConTinued)
modbus CommuniCaTions ConfiguraTion
The Modbus communication settings are accessible 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. SR55
uses only the 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 SR55 system, it allows up to 32 slaves, and one master. Every message begins with the
master 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):
Address
(1 byte)
Function
(1 byte)
Request Data
(n bytes)
CRC
(2 bytes)
slave (response message):
Address
(1 byte)
Function
(1 byte)
Response Data
(n bytes)
CRC
(2 bytes)
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.
CrC
The used method is the CRC-16 (Cyclic Redundancy Check). This field is formed by two bytes;
where first the least significant byte is transmitted (CRC-), and then the most significant
(CRC+). The CRC calculation form is described in the Modbus RTU protocol specification.

Automation Direct Stellar SR55 Series Specifications

General

Brand	Automation Direct
Model	Stellar SR55 Series
Category	Controller
Language	English