Kruger Ecowatt Drive K120 Series, Operation Manual

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Ecowatt ® Drive K120 series Communication protocol
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In a character frame, only the data bits carry information. The start bit, check bit, and
stop bit are used to facilitate the transmission of the data bits to the destination device.
In practical applications, you must set the data bits, parity check bits, and stop bits
consistently.
In RTU mode, a new frame always must be preceded by a time gap with a mini. length
of 3.5 bytes. On a network where the transmission rate is calculated based on the baud
rate, time gap of 3.5 bytes can be easily obtained. After the idle time ends, the data
domains are sent in the following sequence: slave address, operation command code,
data, and CRC check character. Each byte sent in each domain includes hexadecimal
characters (0–9, A–F). The network devices always monitor the communication bus.
After receiving the first domain (address information), each network device identifies
the byte. After the last byte is sent, a similar transmission interval (with a mini. length
of 3.5 bytes) is used to indicate that the frame transmission ends. Then, the
transmission of a new frame starts.
RTU data frame format
Modbus packet
Start with a time gap
(with a min. length of 3.5
bytes)
Slave
address
Function
code
Data Check
End with a time gap
(with a min. length of
3.5 bytes)
The information of a frame must be sent in a continuous data flow. If there is an
interval greater than the transmission time of 1.5 bytes before the transmission of the
entire frame is complete, the receiving device deletes the incomplete information, and
mistakes the subsequent byte for the address domain of a new frame. Similarly, if the
transmission interval between two frames is shorter than the time gap with a min.
length of 3.5 bytes, the receiving device mistakes it for the data of the last frame. The
CRC check value is incorrect due to the disorder of the frames, and thus a
communication fault occurs.
The following table describes the standard structure of an RTU frame.
START (frame header) T1-T2-T3-T4 (time gap with a min. length of 3.5 bytes)
ADDR (slave address
domain)
Communication address: 0–247 (in decimal system) (0
indicates the broadcast address)
CMD (function domain) 03H: read slave parameters
06H: write slave parameters
Data domain
DATA (N-1)
…
DATA (0)
Data of 2*N bytes, main content of the communication as
well as the core of data exchanging
CRC CHK low-order bits
Detection value: CRC (16 bits)
CRC CHK high-order bits
END (frame tail) T1-T2-T3-T4 (time gap with a min. length of 3.5 bytes)