Veichi JT550 Series Manual page 130

Chapter 7 Maintenance and Troubleshooting
The first domain transmitted is device address where hexadecimal is used during the transmission.
Network devices continuously monitor the network bus, including pause intervals. When the first domain
(address domain) receives messages, each device will decode them to decide if the messages are sent to
them. After the last transmitted character, an pause of at least 3.5 characters time indicates the end of a
message. A new message may start after the pause. If a new message is sent out before the pause of 3.5
characters time ends, the receiving device will consider it as a continuation of the previous message. Such
action will lead to an error because the last value of CRC domain is incorrect.
RTU Data Frame Format as below:
Frame Head Slave Address
Data Frame Bits Descriptions:
Frame Head START
Slave Address ADR
Command Codes CMD
Function Codes Address H
Function Codes Address L
Function Codes Count H
Function Codes Count L
Data H
Data L
CRC CHK Low Bit
CRC CHK High Bit
END
1.1.2 Command Codes and Communication Data Description
Inverter supports read and write of word parameters. Operation Command for Read: 0x03; Operation
Command for Write:0x06. Byte or bit read/write operations are not supported.
1) Command Code: 03H, read N words (Up to 12 words).
For example: An inverter's slave address is 01 and its start address is F003. Read 1 word from the
start address, and this frame's structure is described as the following:
Host Command Information:
Slave's Response Message:
Command Codes
Larger than the transmission time of 3.5 characters
Communication Addresses Range：1~247；0＝Broadcast Address
03：Read Slave Parameters；06：Write Slave Parameters
Inverter's built-in parameter address which is represented by hexadecimal is
divided into function code parameters and non-function code parameters.
Please refer to address definitions for more info. While transmitting, high bit is
in front of low bit.
This frame reads the number of function codes. If it's 1, it means 1 function
code is detected. High bit is in front of low bit while transmitting. This
protocol can only rewrite 1 function code.
Response data or data to write in. High bit is in front of low bit while
transmitting.
Detection Value: CRC16 Check Value. Low bit is in front of high bit while
transmitting
Refer to CRC Check Description for calculation methods.
3.5 Characters
ADR
CMD
Start Address High Bit
Start Address Low Bit
Register Count High Bit
Register Count Low Bit
CRC CHK Low Bit
CRC CHK High Bit
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Function Codes
01H
03H
F0H
03H
00H
01H
CRC CHK's value to be
calculated
JT550 Series Inverter Manual
Data Check End