Goodrive300 Series VFD Communication protocol
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else crc_value=crc_value>>1;
} }
return(crc_value);
}
In ladder logic, CKSM calculated the CRC value according to the frame with the table inquiry. The
method is advanced with easy program and quick calculation speed. But the ROM space the program
occupied is huge. So use it with caution according to the program required space.
10.4 RTU command code and communication data illustration
10.4.1 Command code: 03H
03H (correspond to binary 0000 0011), read N words (Word)(Max. continuous reading is 16
words)
Command code 03H means that if the master read data form the VFD, 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 VFD.
For example, read continuous 2 data content from0004H from the VFD 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 VFD)
T1-T2-T3-T4 (transmission time of 3.5 bytes)
High bit of the start bit
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 VFD with the address of 01H and ADDR
occupies one byte
CMD=03H means the command message is sent to read data form the VFD and CMD occupies one
byte
"Start address" means reading data form the address and it occupies 2 bytes with the fact that the
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