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MODBUS
FORCE SINGLE COIL
PRESET SINGLE
REGISTER
30
distributed over 2 words. In the analog input process image, the first
channel has the value 0x0038, while the second channel has the value
0x3F1B.
Byte Name
Example
Start frame
Slave address 11
Function code 4
Count byte 4
Data 1 high byte 0
Data 1 low byte 56
Data 2 high byte 63
Data 2 low byte 11
Error Check
LRC / CRC
End of frame
Writing a Digital Output (Function 5)
Function 5 can be used to write a digital output. In this example the third
digital output of slave number 11 is written. The digital outputs begin at
offset 0x0000 (hex). The digital value is located in the high byte of the data.
To switch the output on, "Data high" must contain 0xFF (hex), while 0x00
(hex) is used to switch the output off again. "Data low" must contain 0x00
(hex).
Query
Byte Name
Example
Start frame
Slave address 11
Function code 5
Start address high 0
Start address low 2
Data high 255
Data low 0
Error Check
LRC / CRC
End of frame
Response
The Bus Terminal Controller answers with the same telegram.
Byte Name
Example
Start frame
Slave address 11
Function code 5
Start address high 0
Start address low 2
Data high 255
Data low 0
Error Check
LRC / CRC
End of frame
Writing an Analog Output (Function 6)
Function 6 can be used to access the output process image and the
interface.
The first analog output of slave number 11 is written with function 6. The
analog outputs begin at offset 0x0800 (hex). Here again the offset always
describes a word. This means offset 0x0803 refers to the fourth word in the
output process image.
RTU
ASCII
„:"
0x3A
0x0B
„0B"
0x30, 0x42
0x04
„04"
0x30, 0x34
0x04
„04"
0x30, 0x30
0x00
„00"
0x30, 0x30
0x38
„38"
0x33, 0x38
0x3F
„3F"
0x33, 0x46
0x0B
„0B"
0x30, 0x42
0x80
„6A"
0x36, 0x41
0x7E
t1-t2-t3
CRLF
0xD, 0xA
RTU
ASCII
„:"
0x3A
0x0B
„0B"
0x30, 0x42
0x05
„05"
0x30, 0x35
0x00
„00"
0x30, 0x30
0x02
„02"
0x30, 0x32
0xFF
„FF"
0x46, 0x46
0x00
„00"
0x30, 0x32
0x2D
„EF"
0x45, 0x46
0x50
t1-t2-t3
CRLF
0xD, 0xA
RTU
ASCII
„:"
0x3A
0x0B
„0B"
0x30, 0x42
0x05
„05"
0x30, 0x35
0x00
„00"
0x30, 0x30
0x02
„02"
0x30, 0x32
0xFF
„FF"
0x46, 0x46
0x00
„00"
0x30, 0x32
0x2D
„EF"
0x45, 0x46
0x50
t1-t2-t3
CRLF
0xD, 0xA
BC7300
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