Goodrive600 series high-performance multifunction VFD
Communication networking
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6.3.3 RTU command code and communication data
6.3.3.1 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 uses the hexadecimal
system (a number followed by "H" indicates a hexadecimal value). One hexadecimal value occupies one byte.
The command is used to read the parameters and working 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 0004H to 0005H) of the VFD whose address is 01H, 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 high-order bit
00H
Start address low-order bit
04H
Data count high-order bit
00H
Data count low-order bit
02H
CRC low-order bit
85H
CRC high-order bit
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. "ADDR" occupies one byte.
"CMD" is "03H", indicating that the command is used to read data from the VFD. "CMD" occupies one byte.
"Start address" indicates that data reading is started from this address. It occupies two bytes, with the high-order bit on
the left and low-order bit on the right.
"Data count" indicates the count of data to be read (unit: word). "Start address" is "0004H" and "Data count" is 0002H,
indicating that data is to be read from the data addresses of 0004H and 0005H.
CRC check occupies two bytes, with the low-order bit on the left and high-order bit on the right.
RTU slave response (sent from the VFD to the master):
START
T1-T2-T3-T4 (time gap with a min. length of 3.5 bytes)
ADDR
01H
CMD
03H
Number of bytes
04H
High-order bit of data in 0004H
13H
Low-order bit of data in 0004H
88H
High-order bit of data in 0005H
00H
Low-order bit of data in 0005H
00H
CRC low-order bits
7EH
CRC high-order bits
9DH
END
T1-T2-T3-T4 (time gap with a min. length of 3.5 bytes)
The definition of the response information is described as follows:
