Emheater EM12 Series, Руководство пользователя

Страница: 128 / 166

EM12 User’s Manual Appendix I
123
Target
station
address
Read the
command
(0x83)
Error type
CRC
correction and
L
……
H
Free
>3.5Byte 1Byte
1Byte
1Byte
2Byte
Calculate CRC
correction
Slave reads and
response error
frame
Free
(Start frame)
Target
station
address
Write the
command
(0x86)
Error type
CRC
correction and
L
……
H
Free
>3.5Byte 1Byte
1Byte
1Byte
2Byte
Calculate CRC
correction
Slave writes and
response error
frame
Free
(Start frame)
Error types
：
01-Command code error
02-Address error
03-Data error
04-Command cannot to process
RTU frame format
Frame start (START) More than the 3.5- character time
Slave address(ADR) Communication address:1 to 247(0: broadcast address)
Command code(CMD)
03: Read slave parameters
06: Write slave parameters
Function code address(H)
It indicates the external parameter address of frequency inverter in
hexadecimal format;
There are functional code or non-functional code (such as running state
parameter/ running command parameters) type parameters, for details
see the address definition.
During the transmission, high bit is put in the front, and low bit is at the
back.
Function code address(L)
Number of function code(H)
It indicates the number of function code ready by the frame. If it is “1”,
then it indicates that it reads one function code. During the transmission,
high bit is put in the front, and low bit is at the back.
Only one function code can be modified at one time without the field.
Number of function code(L)
Data(H) It indicates the replying data or the data waiting to write-in. During the
transmission, high bit is put in the front, and low bit is at the back.
Data(L)
END 3.5- character time
CRC Checking
In RTU mode, messages include an error-checking field that is based on a CRC method. The CRC field checks the
contents of the entire message. The CRC field is two bytes, containing a16-bit binary value. The CRC value is
calculated by the transmitting device, which appends the CRC to the message. The receiving device recalculates a
CRC during receipt of the message, and compares the calculated value to the actual value it received in the CRC
field.
If the two values are not equal, that means transmission is error
The CRC is started by 0xFFFF.Then a process begins of applying successive eight-bit bytes of the message to the
current contents of the register. Only the eight bits of data in each character are used for generating the CRC. Start
and stop bits, and the parity bit, do not apply to the CRC. During generation of the CRC, each eight-bit character