Inovance MD500

Appendix B
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146
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B.3 Data Format
The Modbus-RTU protocol communication data format of the drive is as follows. The drive supports reading
and writing of word-type parameters only. Reading command is 0x03 and writing command is 0x06. It does not
support reading and writing of bytes or bits.
Function code
H----L
CRC and
L----H
Idle
Frame of reading
command from the
master
Idle (frame header)
1
byte 1 byte 2
byte 2 byte 2 byte> 3
.5 byte
Calculate CRC
Target
station
address
Read
command
0x03
Number of
function
codes (n)
In theory, the host computer can read several consecutive parameters (n can reach up to 12) but the last pa-
rameter it reads must not jump to the next parameter group. Otherwise, an error occurs on response.
Function code
H----L
CRC and
L----H
Idle
Frame of reading
response from
the slave
1 byte 1 byte (2n)
byte1 byte
2 byte> 3.5 byte
Calculate CRC
Idle (frame header)
Read
command
0x03
Target
station
address
Number
of bytes
(2n)
Parameter
address
H----L
Function
parameter
H----L
CRC and
L----H
Idle
Frame of writing
command from
the master
Idle (frame header)
1 byte 1 byte 2 byte 2 byte> 3.5 byte 2 byte
Calculate CRC
Target
station
address
Write
command
0x06
Parameter
address
H----L
Function
parameter
H----L
CRC and
L----H
Idle
Frame of writing
response from
the slave
Idle
1 byte 1 byte 2 byte 2 byte> 3.5 byte 2 byte
Calculate CRC
Target
station
address
Write
command
0x06
If the slave detects reading/writing failure caused by a communication frame error or by other reasons, an error
frame will be returned.
0x83
Error
type
CRC and
L----H
Idle
Frame of reading
response error from
the slave
Idle (frame header)
1 byte 1 byte> 3.5 byte 2 byte
Calculate CRC
1 byte
0x86
Error
type
CRC and
L----H
Idle
Frame of writing
response error from
the slave
1Byte 1Byte>3.5Byte 2Byte
Calculate CRC
1Byte
Error type:
01: Command code error
02: Address error
03: Data error
04: Command cannot be handled
Idle (frame header)
Target
station
address
Target
station
address