Goodrive350-19 series VFD Communication protocols
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In the ladder logic, CKSM uses the table look-up method to calculate the CRC value according to the
content in the frame. The program of this method is simple, and the calculation is fast, but the ROM
space occupied is large. Use this program with caution in scenarios where there are space
occupation requirements on programs.
10.4 RTU command code and communication data
10.4.1 Command code 03H, reading N words (continuously up to 16 words)
The command code 03H is used by the master to read data from the VFD. The count of data to be
read depends on the "data count" in the command. A maximum of 16 pieces of data can be read. The
addresses of the read parameters must be contiguous. Each piece of data occupies 2 bytes, that is,
one word. The command format is presented using the hexadecimal system (a number followed by
"H" indicates a hexadecimal value). One hexadecimal value occupies one byte.
The 03H command is used to read information including the parameters and running status of the
VFD.
For example, starting from the data address of 0004H, to read two contiguous pieces of data (that is,
to read content from the data addresses 0004H and 0005H), the frame structures are described in the
following.
RTU master command (sent from the master to the VFD):
START
T1-T2-T3-T4 (time gap with a min. length of 3.5 bytes)
ADDR (address)
01H
CMD (command code)
03H
Start address MSB
00H
Start address LSB
04H
Data count MSB
00H
Data count LSB
02H
CRC LSB
85H
CRC MSB
CAH
END
T1-T2-T3-T4 (time gap with a min. length of 3.5 bytes)
"START" and "END" are "T1-T2-T3-T4 (time gap with a min. length of 3.5 bytes)", indicating that a
time gap with a minimum length of 3.5 bytes must be kept before RS485 communication is executed.
The time gap is used to distinguish one message from another so that the two messages are not
regarded as one message.
"ADDR" is "01H", indicating that the command is sent to the VFD whose address is 01H. The ADDR
information occupies one byte.
"CMD" is "03H", indicating that the command is used to read data from the VFD. The CMD
information occupies one byte.
"Start address" indicates that data reading is started from this address. It occupies two bytes, with the