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APPENDIX C
Communication Protocols
Introduction
The hardware interface and software protocol are defined for performing serial
communications with the Viltech using the Modbus RTU protocol. In this case, the
implementation of the protocol is limited to the sub-set of the complete set of possible
message types. Communications with one or more compressors is possible using a RS-
485 or RS-422 multi-drop interface.
NOTE: Modbus is a registered trademark of Modicon, Inc.
Real time monitoring of the following data is provided:
• Analog input parameters
• Discrete I/O parameters
• Mode and State information
• Computed parameters
• Alarm Information
Real time control of the following parameters is provided:
• Compressor Control including start/stop and mode changes
• Compressor Capacity Control Setpoints
Applicable Documents
Familiarity with the following documents is highly recommended:
• Modicon Modbus Protocol Reference Guide (PI-MBUS300)
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