VEGA VEGACOM 557 Modbus protocol - Manual (Page 34)

34 VEGACOM 557 Modbus
Setup of VEGACOM 557
5 Setup
5.1 Setup check list:
Proceed with the setup of VEGACOM 557 on
Modbus as follows:
I. Check hardware requirements:
• Modbus-compatible Master component
(Modus: RTU or ASCII)
• Check interface type (RS 232, RS 485,
RS 422 or TTY)
• VEGACOM 557 version "Modbus“
II. Carry out adjustments on VEGACOM
557 (DIL switch on additional board):
• Adjust mode for Modbus
• Activate interface type
• Set parameter for interface
• Set Modbus address
III. Make connection to Modbus and check
communication:
• In case of correct communication, the
green LED marked "BA“ lights on VEGA-
COM 557.
5.2 Communication structure
Within the data communication between
VEGACOM 557 and the connected process-
ing system, the following functions are sup-
ported:
- Mode (VEGACOM 557 is Slave)
- Instrument address (default value # 1)
- Enquiries:
Function 01, Read Coil Status
Function 02, Read Input Status
Function 04, Read Input Register(s)
- Diagnostics
Function 08, Loop back Diagnostic
The RTU mode or the ASCII mode are used
as transmission mode.
Thereby any DCS value transmitted by
VEGACOM is represented by a register
address (= 2 register words = 4 Byte):
- 2 Byte indication value
- 1 Byte unit (is filled with 0)
- 1 Byte status information
VEGACOM 557 does not transfer the decimal
point as well as the unit of measurement of
the DCS value to the Modbus.
This information must be completed by the
user with the software of the process data
processing.
Content of the enquiry telegram
(Modbus-Master –> VEGACOM 557):
• Instrument address VEGACOM on Mod-
bus
• Function code
• Address of the 1. register (Modicon regis-
ter memory)
• Number of registers
• Checksum (error control)
Content of the answering telegram
(VEGACOM 557 –> Modbus-Master):
• Instrument address VEGACOM on Mod-
bus
• Function code
• Number of register data bytes
• Register data
• Checksum (error control)