Modbus Mode - Ebyte E810-DTU User Manual

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4.2.4 Modbus mode

Modbus conversion mode supports RTU conversion mode. The E810-DTU(CAN-RS485) module is used as a slave
device to receive and respond to commands sent by the host (via the UART).
The E810-DTU(CAN-RS485) conversion module supports two Modbus commands: read register (function code 03)
and write multiple registers (function code 16).
A buffer is internally built in the conversion module for buffering the received CAN frame data, and the buffer has a
total of 64 levels of buffer according to the addresses 0~63. The cache address starts from 0 to address 63, and can
continuously buffer 8 frames of CAN data (8 bytes per frame, a total of 64 bytes). When the first frame of CAN data is
received, the CAN frame data is stored in address 0, and the received CAN frame data is sequentially stored in increasing
order according to the address. If the 64-level cache is full, the newly received CAN frame data will be stored in address
0 and overwrite the original number, following FIFO.
Read register (function code 03):
Send command:
[Device Address] [Command No. 03 (0x03)] [Start Register Address is 8 Bits High] [8 Bits Low] [Read Register
Numbers is 8 Bits High] [8 Bits Low]
[High 8 bits of CRC check] [Lower 8 bits of CRC check]
The read format is only allowed
00 – 00 07 address is read), after reading successfully, the 8 The byte data will be emptied, and the data after its address
will move forward by 8 data.
such as:
When the module in MODBUS mode, the CAN bus receives 4 frames of data:
First frame: 0x01 0x02 0x03 0x04 Total: 4 bytes of data
Second frame: 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F Total: 6 bytes of data
Third frame: 0x11 0x22 0x33 0x44 0x55 0x66 0x77 0x88 Total:8 bytes of data
Fourth frame: 0XAA 0XBB 0XCC Total: 3 bytes of data
They are stored in the MODBUS cache address:
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to read 00 08 from address 00 00 (one byte of data is read at a time, that is, data of 00
E810-DTU(CAN-RS485) User Manual
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