Best E5 Series User Manual page 194

Chapter 7 Modbus Maintenance
3. Communication Mode
1） Drive is used as a slave for master-slave point-to-point communication. When master
sends commands using broadcast address, the slave does not respond;
2） Native address, baud rate and data format of inverter are set through slave operating
panel or serial communication;
3） Slave reports the current fault information in the latest response frame for master polling;
4） Drive employs RS-485 interface mode.
4. Protocol Format
Modbus protocol supports both RTU and ASCII mode.
RTU data frame format is shown as the figure below:
Start: at
起始:
least 3.5 idle
至少3.5个
characters
字符空闲
RTU:
In RTU mode, idle time between frames can be set through function code or comply with
Modbus internal convention, for which the minimum interframe idle is as follows:
1） Frame header and end define the frame by making bus idle time equal to or longer
than 3.5-byte time;
2） After the start of frame, the clearance between characters must be less than
1.5-character communication time, or the newly received characters will be treated
as the header of the new frame;
3） Data check employs CRC-16 and the whole information participates in the check;
the high and low bytes of check sum shall be sent after exchange. Please refer to
examples at the end of protocol for details of CRC check;
4） The bus idle time of at least 3.5 characters (or set minimum bus idle time) shall be
maintained between frames and needs not to accumulate the starting and ending
idle time.
The data frame of which the request frame is "reading parameter 002 of #1 machine" is as
below:
RTU data frame format
Slave
Parameter
从机地址 功能码
address
RTU数据帧格式
Modbus message
Modbus报文
Data
数据
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E5 User Manual
结束:
End: at least
Check
3.5 idle
校验 至少3.5个
characters
字符空闲