Rtu Command Code And Communication Data; Command Code 03H - INVT Goodrive20-UL VFD Series Operation Manual

Goodrive20-UL Series VFD
if(crc_value&0x0001)crc_value=(crc_value>>1)^0xa001;
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.

7.3 RTU command code and communication data

7.3.1 Command code 03H

03H (correspond to binary 0000 0011), reading N words (continuously up to 16 words)
Command code 03H means that if the master read data from 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)
START
ADDR
CMD
High bit of the start address
Low bit of the start address
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.
}
T1-T2-T3-T4
01H
03H
00H
04H
00H
02H
85H
CAH
T1-T2-T3-T4
-119-
Communication protocol