VEGA VEGABAR 81 Modbus and Levelmaster protocol - Operating Instructions - Manual (Page 64)

64
10 Supplement
VEGABAR 81 • Modbus and Levelmaster protocol
46293-EN-131107
and serial (EIA-232 and EIA-485) as well as the modes ASCII, TCP and RTU are available for the
data transfer. In the RTU and ASCII mode interesting here, data will be transmitted in binary form.
The telegram consists generally of the address, the function, the data as well as the transmission
check.
Bus architecture
In the version Modbus RTU, up to 32 participants can be connected to the bus. The length of the
twisted two-wire cable can be up to 1200 m. The bus must be terminated on both sides at the last
bus participant with a terminating resistor of 120 Ohm. The resistor is already integrated in the
VEGABAR 81 and is activated/deactivated via a slide switch.
4
1
3 3 3
2
+
+
power supply
MODBUS
D0 D1 IS GN
D
USB
+
+
power supply
MODBUS
D0 D1 IS GN
D
USB
+
+
power supply
MODBUS
D0 D1 IS GN
D
USB
1 3 4 5 2 off on ( )
(
)
(-)
(-) 1 3 4 5 2 off on ( )
(
)
(-)
(-) 1 3 4 5 2 off on ( )
(
)
(-)
(-)
Fig. 33: Bus architecture Modbus
1 RTU
2 Connection resistor
3 Bus participant
4 Voltage supply
Protocol description
The VEGABAR 81 is suitable for connection to the following RTUs with Modbus RTU or ASCII
protocol.
RTU Protocol
ABB Totalflow Modbus RTU, ASCII
Bristol ControlWaveMicro Modbus RTU, ASCII
Fisher ROC Modbus RTU, ASCII
ScadaPack Modbus RTU, ASCII
Thermo Electron Autopilot Modbus RTU, ASCII
Parameters for the bus communication
The VEGABAR 81 is preset with the default values:
Parameter Configurable Values Default Value
Baud Rate 1200, 2400, 4800, 9600, 19200 9600