ProSoft Technology MVI69-MCM - Manual (Page 106)

Reference MVI69-MCM ♦ CompactLogix or MicroLogix Platform
User Manual Modbus Communication Module
Page 106 of 167 ProSoft Technology, Inc.
March 22, 2011
5.2 Functional Overview
5.2.1 About the MODBUS Protocol
MODBUS is a widely-used protocol originally developed by Modicon in 1978.
Since that time, the protocol has been adopted as a standard throughout the
automation industry.
The original MODBUS specification uses a serial connection to communicate
commands and data between Master and Slave devices on a network. Later
enhancements to the protocol allow communication over other types of networks.
MODBUS is a Master/Slave protocol. The Master establishes a connection to the
remote Slave. When the connection is established, the Master sends the
MODBUS commands to the Slave. The MVI69-MCM module can work as a
Master and as a Slave.
The MVI69-MCM module also works as an input/output module between itself
and the Rockwell Automation backplane and processor. The module uses an
internal database to pass data and commands between the processor and
Master and Slave devices on MODBUS networks.
5.2.2 Module Power Up
On power up the module begins performing the following logical functions:
1 Initialize hardware components
o
Initialize CompactLogix or MicroLogix backplane driver
o
Test and Clear all RAM
o
Initialize the serial communication ports
2 Module configuration
3 Initialize Module Register space
4 Enable Slave Driver on selected ports
5 Enable Master Driver on selected ports
After this initialization procedure is complete, the module will begin
communicating with other nodes on the network, depending on the configuration.