➢ Function code 03H: read register data
For example: read the U0-05 register address H1005 (bus voltage).
RTU mode:
➢ Function code06H: write the data in the register
For example: write 300 rpm to the address of P3-18 register of inching speed.
RTU mode:
4. Parity code
RTU mode: double byte hexadecimal number.
The CRC field is a two-byte, 16-bit binary value. It is calculated by the sender and added to the
message; when it is added, it is first the low byte and then the high byte, so the high byte of CRC is the
last byte of the sent message. The receiving device recalculates the CRC of the received message and
compares it with the value in the received CRC field. If the two values are different, there is an error in
the received message, discards the message frame, makes no response, and continues to receive the
data of the next frame. Refer to the description of Modbus protocol for CRC verification calculation
method.
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