VEGA VEGACOM 557 Modbus protocol - Manual (Page 37)

VEGACOM 557 Modbus 37
Data transmission with Modbus RTU
Start
Slave
ad-
dress
Func-
tion
code
Address of the
1. register
word
Number of
register
words
Error
Check
End
Number
of Bytes
Value
range
Meaning
Structure of the meas. value enquiry Modbus-Master to VEGACOM 557
RTU enquiry telegram acc. to measured values (function code 04)
3 ... 4 1 1 2 2 2 3 ... 4
Closed level 1 .. 247 04 0 ... 65.509 1 ... 127 CRC Closed level
0x01 0x04 0x00 0x1C 0x00 0x02 0xXX 0xXX
Start
Slave
ad-
dress
Func-
tion
code
No. of
data
bytes
Error
Check
End
Number
of Bytes
Value
range
Structure of the answer VEGACOM 557 to Modbus-Master
RTU answering telegram (function code 04)
3 ... 4 1 1 1
2 bytes per
register word
2 3 ... 4
Closed level
1 .. 247 04
2 ....
255
0 ... 255 per byte CRC Closed level
0x01 0x04 0x04 0x01 0x4A 0x00 0x00 0xXX
Data (DCS values)
0xXX
DCS value 1 of VEGAMET #2:
Status:
0x00
Unit:
0x00
Meas. value:
0x014A = 3,30%
Procedure with Modbus-Master-simulation (e.g. PC) Procedure with Modbus-Master-simulation (e.g. PC) Procedure with Modbus-Master-simulation (e.g. PC) Procedure with Modbus-Master-simulation (e.g. PC) Procedure with Modbus-Master-simulation (e.g. PC)
In case the data enquiry should be made via a Modbus-Master-simulation, this can be done,
for example, via a self-written communication driver using the "Function code 04 = Read Input
Registers“. The following demonstration should explain the communication processes between
Modbus-Master and VEGACOM 557 on the Modbus.
Example for data from VEGAMET 514:
A DCS value should be collected from VEGAMET #2 (DCS output 1). VEGACOM 557 operates
in mode "Sort measured values acc. to VEGAMET addresses“. The Slave-address of VEGA-
COM 557 is set to 1.
Current meas. value on VEGAMET DCS output 1 is: 3.30% (= 0x014A)
Meaning