M&M RWB series - APPENDIX C Communication Protocols; Introduction; Applicable Documents

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M&M

EFRIGERATION

. C-1

APPENDIX C

Communication Protocols

Introduction

The hardware interface and software protocol are defined for per-

forming serial communications with the M&M Screw Compressor

Computer Control System (CCS). Two open protocols are defined

in this document, Modbus RTU and Allen-Bradley (AB) DF1. In

each case, the implementation of each protocol is limited to the

sub-set of the complete set of possible message types. Communi-

cations with one or more compressors is possible using a multi-

drop RS-422 interface. M&M Refrigeration also supports its own

internal communications protocol which is available upon request.

 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

• Economizer Control (optional)

Applicable Documents

Familiarity with the following documents is highly recommended:

• M&M Refrigeration CCS Screw Compressor Overview

• Modicon Modbus Protocol Reference Guide (PI-MBUS-

300)

• Allen-Bradley DF1 Protocol and Command Set (1770-

6.5.16)

• Allen-Bradley Enhanced and Ethernet PLC-5 Programma-

ble Controllers (1785-6.5.12)