IMO iDrive2 XKL Instruction Manual page 73

iDrive2 inverters
rate and digital check bit in RS485 should be the same and there should be no repeated address.
7.2.2 RTU mode
7.2.2.1 RTU communication frame format
If the controller is set to communicate by RTU mode in Modbus network every 8bit byte in the message includes
two 4Bit hex characters. Compared with ACSII mode, this mode can send more data at the same baud rate.
Code system
· 1 start bit
· 7 or 8 digital bit, the minimum valid bit can be sent firstly. Every 8 bit frame includes two hex characters (0...9,
A...F)
· 1 even/odd check bit . If there is no checkout, the even/odd check bit is inexistent.
· 1 end bit (with checkout), 2 Bit (no checkout).
Error detection field
· CRC
The data format is illustrated as below:
11-bit character frame (BIT1~BIT8 are the digital bits)
Start bit BIT1
10-bit character frame (BIT1~BIT7 are the digital bits)
Start bit BIT1
In one character frame, the digital bit takes effect. The start bit, check bit and end bit is used to send the digital bit
right to the other device. The digital bit, even/odd checkout and end bit should be set as the same in real
application.
The Modbus minimum idle time between frames should be no less than 3.5 bytes. The network device is detecting,
even during the interval time, the network bus. When the first field (the address field) is received, the
corresponding device decodes next transmitting character. When the interval time is at least 3.5 byte, the
message ends.
The whole message frame in RTU mode is a continuous transmitting flow. If there is an interval time (more than
1.5 bytes) before the completion of the frame, the receiving device will renew the uncompleted message and
suppose the next byte as the address field of the new message. As such, if the new message follows the previous
one within the interval time of 3.5 bytes, the receiving device will deal with it as the same with the previous
message. If these two phenomena all happen during the transmission, the CRC will generate a fault message to
respond to the sending devices.
The standard structure of RTU frame:
START
ADDR
CMD
DATA (N-1)
...
DATA (0)
CRC CHK low bit
CRC CHK high bit
BIT2 BIT3 BIT4
BIT2 BIT3 BIT4
T1-T2-T3-T4(transmission time of 3.5 bytes)
Communication address: 0~247(decimal system)(0 is the broadcast address)
03H:read slave parameters
06H:write slave parameters
The data of 2*N bytes are the main content of the communication as well as the
core of data exchanging
Detection value:CRC (16BIT）
BIT5 BIT6 BIT7
BIT5 BIT6
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Communication protocol
BIT8 Check bit End bit
BIT7 Check bit End bit