ProSoft Technology MVI46-MCM - Manual (Page 60)

Reference MVI46-MCM ♦ SLC Platform
User Manual Modbus Communication Module
Page 60 of 108 ProSoft Technology, Inc.
March 29, 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 MVI46-MCM module can work as a
Master and as a Slave.
The MVI46-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 General Concepts
The following topics describe several concepts that are important for
understanding the operation of the MVI46-MCM module.
1 On power up the module begins performing the following logical functions:
2 Initialize hardware components
o
Initialize SLC backplane driver
o Test and Clear all RAM
o Initialize the serial communication ports
3 Wait for module configuration from the SLC processor
4 Allocate and initialize Module Register space
5 Enable Slave Driver on selected ports
6 Enable Master Driver on selected port if configured
After the module has received the Module Configuration, the module will begin
communicating with other nodes on the network, depending on the configuration.