ProSoft Technology MVI46-MCM - Manual (Page 61)

MVI46-MCM ♦ SLC Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 61 of 108
March 29, 2011
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.
Main Logic Loop
Upon completing the power up configuration process, the module enters an
infinite loop that performs the following functions: