Rtu Command Code And Communication Data Illustration - INVT Goodrive3000 GD3000-01-055G-12 Operation Manual

Goodrive3000 series medium voltage inverters

8.4 RTU command code and communication data illustration

8.4.1 Command code: 03H, read N words (Max. continuous reading is 16
words)
Command code 03H means that if the master read data for 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
ADDR
CMD
High bit of the start bit
Low bit of the start bit
High bit of data number
Low bit of data number
CRC low bit
CRC high bit
END
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 low bit is in the front and the high bit is in the behind.
RTU slave response message (from the inverter to the master)
START
ADDR
CMD
Byte number
Data high bit of address 0004H
Data low bit of address 0004H
Data high bit of address 0005H
Data low bit of address 0005H
CRC low bit
CRC high bit
END
The meaning of the response is that:
T1-T2-T3-T4 (transmission time of 3.5 bytes)
01H
03H
00H
04H
00H
02H
85H
CAH
T1-T2-T3-T4 (transmission time of 3.5 bytes)
T1-T2-T3-T4 (transmission time of 3.5 bytes)
T1-T2-T3-T4 (transmission time of 3.5 bytes)
-205-
MODBUS protocol
01H
03H
04H
13H
88H
00H
00H
7EH
9DH