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3 Modbus protocol description
3.6.1 Reading n words
This function is used to read n words starting at a specific address.
Data request
Response
Example
Read measured value (here: 25.0) from the analog input (from word address 0x7000, 4 bytes = 2 words):
chapter 3.7.2 "Float values", Page 20
chapter 3.8 "Checksum (CRC16)", Page 22
Slave address Function
0x03 or 0x04
Address of
first word
Number of words Checksum CRC
1 byte 1 byte 2 bytes 2 bytes 2 bytes
Slave address Function
0x03 or 0x04
Number
of bytes read
Word value(s) Checksum CRC
1 byte 1 byte 1 byte x bytes 2 bytes
Data request:
01 03 70 00 00 02 DE CB
Slave Function Address of
1st word
Number of words CRC
Response (measured value in Modbus floating-point format):
01 03 04 00 00 41 C8 CB F5
Slave Function Bytes
read
Measured value CRC
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