ProSoft Technology MVI69E-MBS - Manual (Page 114)

Reference MVI69E-MBS ♦ CompactLogix Platform
User Manual Communication Module
Page 114 of 162 ProSoft Technology, Inc.
January 6, 2014
7.2 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 MVI69E-MBS module can work as a Master and as
a Slave.
The MVI69E-MBS 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.
Modbus Master
A port configured as a virtual Modbus Master actively issues Modbus commands
to other nodes on the Modbus network, supporting up to 250 commands on each
port. The Master ports have an optimized polling characteristic that polls slaves
with communication problems less frequently.
Command List Up to 250 commands per Master port, each fully
configurable for function, slave address, register to/from
addressing and word/bit count.
Polling of command list Configurable polling of command list, including continuous
and on change of data, and dynamically user or automatic
enabled.
Status Data Error codes available on an individual command basis. In
addition, a slave status list is maintained per active
Modbus Master port.
Modbus Slave
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 CompactLogix
processor.
Node address 1 to 247 (software selectable)
Status Data Error codes, counters and port status available per
configured slave port