Kruger Ecowatt K320 Series Operation Manual page 288

Ecowatt Drive K320 series
®
Use shielded cables, if possible, in multi-VFD connection. The baud rates, data bit check
settings, and other basic parameters of all the devices on the RS485 line must be set
consistently, and addresses cannot be repeated.
9.3.2 RTU
9.3.2.1 RTU communication frame structure
When a controller is set to use the RTU communication mode on a Modbus network, every
byte (8 bits) in the message includes 2 hexadecimal characters (each includes 4 bits).
Compared with the ASCII mode, the RTU mode can help to send more data at the same baud
rate.
Code system
• 1 start bit
• 7 or 8 data bits; the minimum valid bit is sent first. Each frame domain of 8 bits includes 2
hexadecimal characters (0–9, A–F).
• 1 odd/even check bit; this bit is not provided if no check is needed.
• 1 stop bit (with check performed), or 2 bits (without check)
Error detection domain
• Cyclic redundancy check (CRC)
The following table describes the data format.
11-bit character frame (Bits 1 to 8 are data bits)
Start bit BIT1
10-bit character frame (Bits 1 to 7 are data bits)
Start bit BIT1
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 minimum length of
3.5 bytes. On a network where the transmission rate is calculated based on the baud rate, the
transmission time 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 minimum length of 3.5 bytes) is used to indicate
that the frame transmission ends. Then, the transmission of a new frame starts.
BIT2 BIT3 BIT4
BIT2 BIT3 BIT4
BIT5 BIT6 BIT7
BIT5 BIT6
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Communication
BIT8 Check bit Stop bit
BIT7 Check bit Stop bit