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Communication Protocol 111 - 144
9.4 RTU command code and communication data illustration
9.4.1 RTU mode
9.4.1.1Command code: 03H
03H （ correspond to binary 0000 0011), read N words （ Word ） (the Max. continuous reading is 16 words)
Command code 03H means that if the master read data from the inverter, the reading number depends on the
“data number” in the command code. The Max. Continuous reading number is 16 and the parameter address
should be continuous. The byte length of every data is 2 (one word). The following command format is
illustrated by hex (a number with “H” means hex) and one hex occupies one byte.
The command code is used to read the working stage of the inverter.
For example, read continuous 2 data content from 0004H from the inverter with the address of 01H (read the
content of data address of 0004H and 0005H), the frame structure is as below:
RTU master command message (from the master to the inverter)
START T1-T2-T3-T4 (transmission time of 3.5 bytes)
ADDR 01H
CMD 03H
High bit of the start address 00H
Low bit of the start address 04H
High bit of data number 00H
Low bit of data number 02H
CRC low bit 85H
CRC high bit CAH
END T1-T2-T3-T4 (transmission time of 3.5 bytes)
T1-T2-T3-T4 between START and END is to provide at least the time of 3.5 bytes as the leisure time and
distinguish two messages for the avoidance of taking two messages as one message.
ADDR = 01H means the command message is sent to the inverter with the address of 01H and ADDR
occupies one byte
CMD =03H means the command message is sent to read data from the inverter and CMD occupies one byte
“Start address” means reading data from the address and it occupies 2 bytes with the fact that the high bit is
in the front and the low bit is in the behind.
“Data number” means the reading data number with the unit of word. If the “start address’ is 0004H and the
“data number” is 0002H, the data of 0004H and 0005H will be read.
CRC occupies 2 bytes with the fact that the high bit is in the front and the low bit is in the behind.
RTU slave response message (from the inverter to the master)
START T1-T2-T3-T4 (transmission time of 3.5 bytes)
ADDR 01H
CMD 03H
Byte number 04H
Data high bit of address 0004H 13H
Data low bit of address 0004H 88H
Data high bit of address 0005H 00H
Data low bit of address 0005H 00H
CRC CHK low bit 7EH
CRC CHK high bit 9DH
END T1-T2-T3-T4 (transmission time of 3.5 bytes)