Reference MVI56-MCM ♦ ControlLogix Platform
Modbus Communication Module
ProSoft Technology, Inc. Page 87 of 159
July 24, 2008
8.1.4 Functional Specifications
Support for the storage and transfer of up to 5000 registers to/from the
ControlLogix processor's data files
Module memory usage that is completely user definable
Two ports to emulate any combination of Modbus master or slave device
Supports Enron version of Modbus protocol for floating point data
transactions
Slave Specifications
A port configured as a Modbus slave permits a remote master to interact with all
data contained in the module. This data can be derived from other Modbus slave
devices on the network, through a master port, or from the ControlLogix
processor. The MVI56-MCM module accepts Modbus function code commands
of 1, 2, 3, 4, 5, 6, 8, 15, 16, 17, 22 and 23 from an attached Modbus master unit.
Master Specifications
A port configured as a virtual Modbus master device on the MVI56-MCM module
actively issues Modbus commands to other nodes on the Modbus network. One
hundred (100) commands are supported on each port. Additionally, the master
ports have an optimized polling characteristic that polls slaves with
communication problems less frequently. The ControlLogix processor can be
programmed to control the activity on the port by actively selecting commands
from the command list to execute or issuing commands directly from the ladder
logic.
8.2 Functional Overview
This section provides an overview of how the MVI56-MCM module transfers data
using the MCM protocol. You should understand the important concepts in this
chapter before you begin installing and configuring the module.
8.2.1 General Concepts
The following topics describe several concepts that are important for
understanding the operation of the MVI56-MCM module.
On power up the module begins performing the following logical functions:
1 Initialize hardware components
2 Initialize ControlLogix backplane driver
o Test and Clear all RAM
o Initialize the serial communication ports
o Wait for Module Configuration from ControlLogix processor
3 Initialize Module Register space
4 Enable Slave Driver on selected ports
5 Enable Master Driver on selected ports
After the module has received the Module Configuration Block from the
processor, the module will begin communicating with other nodes on the
network, depending on the configuration.
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