GD350A series high-performance multifunction VFD
-286-
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. 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
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
High-order bit of data in 0004H
04H
Low-order bit of data in 0004H
13H
High-order bit of data in 0005H
88H
Low-order bit of data in 0005H
00H
CRC low-order bits
00H
CRC high-order bits
7EH
