GT200 series general purpose inverter instruction manual
Modbus data frame
ASCII mode
Start:
“
0x3A
”
Slave
address
Function
code
Data
Check
End:
“
0xD,0xA
”
Modbus adopts the “Big Endian” coding method, which sends high bit bytes first, and
then low bit bytes.
RTU method: Under RTU method, idle time between frames could select function code
setting or observe inner conventions of Modbus. Min. frame idle agreed inside Modbus is as
follows: Frame head and end use bus idle time larger than or equal to 3.5 bytes to determine
the frame. Data check adopts CRC-16, and the entire information participates in check, while
high and low bits of checksum need to be sent 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:
Add
ress
Function
Code
Register Address
Read Characters
Checksum
0x01
0x03
0x00
0x02
0x00
0x01
0x25
0xCA
The following is response frame of machine 1:
Add
ress
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
88
