Diagnostic message in rtu mode – VEGA VEGASCAN 850 Modbus signal output User Manual
Page 9
Modbus signal output VEGASCAN 850
9
Start
Func-
tion
code
Diagnostic
Code
Diagnostic
Data
Error
Check
End
No. of
bytes
Value
range
Meaning
Structure of the diagnostic function Modbus master to VEGASCAN 850
RTU enquiry telegram diagnostic (function code 08)
3 ... 4
1
1
2
2
2
3 ... 4
Closed level
1 .. 247
08
0
0 ... 65.535
CRC
Closed level
0x01
0x08
0x00
0x00
0xA5
0x37
0xXX
0xXX
Start
Func-
tion
code
Diagnostic
Code
Diagnostic
Data
Error
Check
End
No. of
bytes
Value
range
Meaning
Structure of the acknowledgement of VEGASCAN 850 to Modbus master
RTU acknowledgement telegram diagnostic (function code 08)
3 ... 4
1
1
2
2
2
3 ... 4
Closed level
1 .. 247
08
0
0 ... 65.535
CRC
Closed level
0x01
0x08
0x00
0x00
0xA5
0x37
0xXX
0xXX
Data transmission with Modbus RTU
With the command "Preset Multiple Registers“, the data for the parameter enquiry are trans-
ferred to VEGASCAN. For reading access, 3 register words are necessary and for writing
access, 4 register words.
After VEGASCAN has confirmed the transfer, a cyclical enquiry must be made with a second
command "Read Input Registers“ (function code 04), to get the information that the processing
is finished. VEGASCAN signals an Exception Code "Slave Device Busy“, (0x06) until either the
data has been processed or the processing time has elapsed. As start address are valid,
e.g. 30.500, 31.500 or 32.500, etc. for the Modicon or 499, 1.499 or 2.499, etc. when access-
ing with your own communication driver.
For further information, please contact one of our employees.
Diagnostic message in RTU mode
Function code 08 (diagnostics) enables the diagnostics of the Modbus-participants through
the Modbus-Master. VEGASCAN supports the Diagnostic Code 0x0000 (return of the data). In
the field "Diagnostic Data“ any approved data can be entered, which are returned unchanged
from the functioning VEGASCAN.
Example of a diagnostic telegram:
The Modbus participant with the Slave address 1 shall confirm the diagnostics data 0xA5,
0x37.
Slave
ad-
dress
Slave
ad-
dress