Shenzhen
3onedata Technology Co., Ltd
23
www.3onedata.com
When a CAN-Bus message does not handle Modbus packet, CAN-Bus message using sub protocol. Each
CAN-Bus packet "data 1" are used to fill the segment information (0x81, 0xC2), the information is not converted to
the Modbus RTU frame, only as a frame format is used to verify the information frame. Function code and data
domain values are filled in the CAN-Bus message data from 2 ~ 8.
6.4 Attention Matters
Recommended for use in low speed system, the converter is not suitable for high-speed data transmission.
After the configuration mode and normal mode switch, power must restart, otherwise still is the
implementation of the original work mode, and cannot achieve the success of switching.
In the transparent identity conversion and Modbus RTU conversion, note that the CAN-BUS frame type and
frame type software configuration must be the same, otherwise not successful communication.
In the transparent identity conversion and Modbus RTU conversion, serial frames transmission must meet the
configured time requirements, otherwise it may lead to communication error.
The CAN-BUS is half duplex, so the data conversion process, to ensure orderly on both sides of the bus data.
If both sides at the same time to send a large number of data bus converter, will likely lead to incomplete data
conversion.
Using CAN485 converter, should pay attention to both sides of the bus baud rate and data transmission time
interval rationality, conversion should consider the affordability of the low baud rate of bus data.
For example, when CAN-BUS were converted to serial bus, CAN-BUS can reach the rate of thousands of
frames per second, but the serial bus only to the hundreds of frames per second. So when the CAN-BUS speed too
fast will result in incomplete data conversion.
General CAN-BUS baud rate should be about 3 times the baud rate of serial baud rate, data transmission will
be more uniform. Because in the transmission data on the bus also added other functional domains, equivalent to an
increase of the length of the data, so the same baud rate can transmission time will be longer than the time of serial
bus.
Modbus RTU frame
Address field
08
Function code
11
Data field
00
01
00
02
04
00
0A
01
02
CRC field
ED
69
CAN message
CAN message 1
CAN message 2
Frame information
18
14
Frame ID 1
00
00
Frame ID 2
00
00
Frame ID 3
00
00
Frame ID 4
08
08
Data Field
81
C2
11
0A
00
01
01
02
00
02
04
00
