Inovance MD500T75G - Page 229

MD500 User Manual 8. Interfaces and Communication
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8.5.3 Data Format
The MD500 supports reading and writing of word-type parameters only. The reading command is 0x03 and the writing command is
0x06. It does not support reading and writing of bytes or bits.
The Modbu-RTU protocol communication data format of the MD500 is as follows:
Slave
addr.
Function
code
H----L
Number of
function
codes (n)
CRC and
H----L
Idle
Frame of read
command from
the master
Idle (frame header)
1 byte 1 byte 2 byte 1 byte
2 byte> 3.5 byte
Calculate CRC
Read
command
0x03
In theory, the host computer can read several consecutive parameters (n can reach up to 12) but the last parameter it reads must
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20.
0.00
2.
00
10.
00
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Slave
addr.
Parameter addr.
H----L
Function code
H----L
CRC and
H----L
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
Write
command
0x06
Slave
addr.
Parameter addr.
H----L
Function code
H----L
CRC and
H----L
Idle
Frame of writing
response from the
master
Idle
1 byte 1 byte 2 byte 2 byte> 3.5 byte 2 byte
Calculate CRC
Write
command
0x06
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returned as follows:
Slave
addr.
0x83
Error
type
CRC and
H----L
Idle
Frame of reading response
error from the slave
Idle (frame header)
1 byte 1 byte 1 byte 2 byte> 3.5 byte
Calculate CRC
Slave
addr.
0x86
Error
type
CRC and
H----L
Idle
Frame of writing response
error from the slave
Idle (frame header)
1 byte 1 byte 1 byte 2 byte> 3.5 byte
Calculate CRC
Error type:
01: Command code error
02: Address error
03: Data error
04: Command cannot be handled
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