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RTU mode
In RTU mode, the Modbus minimum idle time between frames should be no less than 3.5 bytes.
The I5000cksum adopts CRC-16 method. All data except I5000cksum itself sent will be counted
into the calculation. Please refer to section: CRC I5000ck for more information.
Note that at least 3.5 bytes of Modbus idle time should be kept and the start and end idle time
need not be summed up to it.
The table below shows the data frame of reading parameter 002 from slave node address 1.
Node addr.
0x01
The table below shows the reply frame from slave node address 1
Node addr.
0x01
ASCII mode
In ASCII mode, the frame head is "0x3A", and default frame tail is "0x0D" or "0x0A". The frame
tail can also be configured by users. Except frame head and tail, other bytes will be sent as
two ASCII characters, first sending higher nibble and then lower nibble. The data have 7/8
bits. "A"~"F" corresponds to the ASCII code of respective capital letter. LRC I5000ck is used.
LRC is calculated by adding all the successive bytes of the message except the head and tail,
discarding any carriers, and then two's complementing the result.
Example of Modbus data frame in ASCII mode:
The command frame of writing 0x0003 into address "0x1000" of slave node address 1 is
shown in the table below:
LRC I5000cksum = the complement of (01+06+10+00+0x00+0x03) = 0xE5
Frame
head
Code
ASCII
3A
Data to write
0
0
30
30
10.4 Protocol function
Command
Data addr.
0x03
0x00
Command
Bytes No.
0x03
Node addr.
0
1
30
31
0
3
30
33
Read No.
0x02
0x00
Data
0x02
0x00
Command
0
6
30
36
LRC
E
5
45
35
112
CRC
0x01
0x25
CRC
0x00
0xB8
Data addr.
1
0
0
31
30
30
Frame tail
CR
0D
0xCA
0x44
0
30
LF
0A
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