Modbus Rtu Conversion; Frame Format - 3onedata CAN485 User Manual

2. CAN-Bus message to serial frame
Assume that CAN-Bus identifies the starting address in the serial frame is 2, the length is 3 (extended frame case),
CAN-Bus message and converted into serial frames results are shown as follows.
Serial frame
Data 1
Data 2
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Data 3
Data 4
Data 5
Data 6
Data 7

6.3 Modbus RTU conversion

Modbus protocol is an application layer protocol is a standard, widely used in various kinds of occasions. The
protocol is open, real-time communication, authentication mechanism is good, very suitable for applications
requiring high reliability communication.
Converter at the serial side using the standard Modbus RTU protocol format, so the converter not only allows users
to use Modbus RTU protocol converter can also directly and other support Modbus RTU protocol device interface.
In the CAN-Bus side, the converter made a simple piecewise format to achieve Modbus communication. The
converter in which the role is still protocol verification and forward transmission, support Modbus protocol, it is not
Modbus host or slave machine, the user can according to the protocol of Modbus communication.

6.3.1 Frame format

Serial bus frame: The serial interface is used in the standard Modbus RTU protocol, so the user can meet the
frame of this Agreement (see Appendix: Modbus protocol). If the transmission frame does not conform to Modbus
RTU format, then the converter will discard the received frame, without conversion.
Modbus RTU transmission format converter uses 1 start bit, 8 data bits, and 1 stop bit.
The maximum length of Modbus RTU frame buffer length: 255 bytes.
CAN-Bus frame: CAN-Bus side of the equipment used to Modbus protocol need to define a reliable transmission
format, where the use of a piecewise protocol, which defines a length greater than 8 bytes of information method
for segmentation and reorganization.
CAN message (standard frame)
Frame information
Frame ID
Data Field
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