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Ecowatt
®
Drive K120 series
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.
7.3 RTU command code and communication data
7.3.1 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 number" 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 command code is used to read the 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 the data addresses 0004H and 0005H) of the VFD
whose slave address is 01H, the frame structures are described in the following.
RTU master command (sent from the
master to the VFD)
START
ADDR (address)
CMD (command
code)
Start address
high-order bit
Start address
low-order bit
Data number
high-order bit
Data number
low-order bit
CRC low-order bit
CRC high-order bit
END
T1-T2-T3-T4
01H
03H
00H
04H
00H
02H
85H
CAH
T1-T2-T3-T4
-131-
RTU slave response (sent from the VFD to
the master)
START
ADDR
CMD
Number of bytes
High-order bit of
data in 0004H
Low-order bit of data
in 0004H
High-order bit of
data in 0005H
Low-order bit of data
in 0005H
CRC CHK low-order
bits
CRC CHK low-order
bits
END
Communication protocol
T1-T2-T3-T4
01H
03H
04H
13H
88H
00H
00H
7EH
9DH
T1-T2-T3-T4
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