VEGA VEGACOM 557 Modbus protocol - Manual (Page 41)

VEGACOM 557 Modbus 41
Diagnostic message in RTU mode
Function code 08 (diagnostics) enables the diagnostics of the Modbus-participants through
the Modbus-Master. VEGACOM 557 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 a functioning VEGACOM 557.
Function 08 is implemented in the same manner for both VEGAMET and VEGALOG.
Example of a diagnostic telegram:
The Modbus participant with the Slave address 1 shall confirm the diagnostic data 0xA5,
0x37.
Data transmission with Modbus RTU
Start
Slave
ad-
dress
Func-
tion
code
Diagnostic
Code
Diagnostic
Data
Error
Check
End
No. of
Bytes
Value
range
Meaning
Structure of the diagnostic function from Modbus master to VEGACOM 557
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
Slave
ad-
dress
Func-
tion
code
Diagnostic
Code
Diagnostic
Data
Error
Check
End
No. of
Bytes
Value
range
Meaning
Structure of the confirmation from VEGACOM 557 to Modbus-Master
RTU confirmation 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