EXPERT Standard Series User Manual
213
after exchange. For detailed CRC check, please refer to examples in the protocol. It is
to be noted that, at least 3.5 characters of bus idle should be kept between frames (or
min. bus idle time should be set), while bus idle between frames need not to
accumulate start and end idles.
The following is data frame requested for reading parameter 002 of machine 1:
Address
Function
Code
Register
Address
Read Characters
Checksum
0x01
0x03
0x00
0x02
0x00
0x01
0x25
0xCA
The following is response frame of machine 1:
Address
Function
Code
Response Bytes
Register Content
Checksum
0x01
0x03
0x02
0x13
0x88
0xB5
0x12
Under ASCII, the frame head is “0x3A”, and the frame end is “0x0D” and “0x0A”
by fault, while the frame end could also be set by users. Under ASCII, except for
frame head and frame end, other data bytes could all be sent in the form of ASCII
code, which are sent to the high 4-bit bytes first, and then to low 4-bit bytes. Under
ASCII, the data has a 7-bit length. As for “A”~“F”, ASCII of capitalized letters of it are
adopted. In this case, data adopts LRC check, which covers information part from
slave address to data. Checksum is equal to the supplementary code of character
sum (abandoning carry bits) of all data participating in check.
An example of Modbus data frame of ASCII is as follows:
Write 4000 (0xFA0) into the inner register 002 of slave 1, the format of command
frame is shown in the following table:
LRC check=supplementary code of (01+06+00+02+0x0F+0xA0)=0x48
Frame
Head
Addres
s
Function
Code
Register
Address
Write
Content
LRC
Check
Frame
End
Character
:
0
1
0
6
0 0 0 2 0 F A 0 4 8 CR LF
ASCII
3A
30 31 30 36 30 30 30 32 30 46 41 30 34 38 0D 0A
The drive, via function code, could set different response delays to adapt to
detailed application needs of various master station, for RTU mode, actual response
delay is not less than an interval of 3.5 characters, for ASCII mode, actual response
delay is not less than 1ms.