VM600 networking manual MAVM600-NET/E 8 - 1
Edition 9 - February 2018
Introduction
SETTING UP A MODBUS CONNECTION (CPUM SW VERSION 067 OR EARLIER)
8 SETTING UP A MODBUS CONNECTION
(CPUM FIRMWARE VERSION 067 OR EARLIER)
8.1 Introduction
This chapter describes the implementation of the Modbus software interface for VM600 racks
as used by CPUM cards running firmware version 067 or earlier.
Most, but not all, Modbus registers are available to CPUM cards running firmware
version 067 or earlier. The tables in Appendix A: MPC4 Modbus register definitions and
Appendix B: AMC8 Modbus register definitions include a column (CPUM < 71) that indicates
which Modbus registers are available in a particular CPUM firmware version.
NOTE: A more flexible implementation of the Modbus server is available for CPUM cards
running firmware version 071 or later (see 9 Setting up a Modbus connection
(CPUM firmware version 071 or later)).
The Modbus software interface provides a Modbus server for a VM600 rack that
communicates with the following VM600 cards:
•MPC4
•AMC8.
The transmitted data consists of real-time values (vibration level, pressure and so on), status
and configuration information (such as alarms). This data can be used by any external
system, such as a distributed control system (DCS), for the purposes of machinery
monitoring.
See Appendix A: MPC4 Modbus register definitions for detailed MPC4 Modbus register
mapping information and Appendix B: AMC8 Modbus register definitions for detailed AMC8
Modbus register mapping information.
8.2 Modbus
Modbus started in the 1970s as a serial communications protocol published by Modicon for
use with programmable logic controllers (PLCs). On a Modbus network, controllers
communicate using a master-slave technique, in which only one device (the master) can
initiate queries (transactions). The other devices on the network (the slaves) respond by
supplying the requested data to the master, or by taking the action requested in the query.
Since then, Modbus has evolved into become one of the most widely used standards in
industrial automation and control. It has become an application layer messaging protocol for
client-server communication between devices connected on different types of buses or
networks. However, it is still mainly used to exchange data in the field of automation.
Today, Modbus is a client-server protocol based on transactions (see Figure 8-1), which
consist of:
• a request issued by the client
• a response issued by the server.
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