About The Modbus Protocol; Modbus Master; Modbus Slave - ProSoft MVI69E-MBS User Manual

MVI69E-MBS ♦ CompactLogix Platform
Modbus Serial Enhanced Communication Module
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 CompactLogix or MicroLogix 1500-
LRP processor. The module uses an internal database to pass data and
commands between the processor and Master and Slave devices on Modbus
networks.

7.2.1 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
Polling of command list
Status Data

7.2.2 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 or
MicroLogix 1500-LRP processor.
Node address
Status Data
ProSoft Technology, Inc.
June 28, 2017
Up to 250 commands per Master port, each fully
configurable for function, slave address, register to/from
addressing and word/bit count.
Configurable polling of command list, including continuous
and on change of data, and dynamically user or automatic
enabled.
Error codes available on an individual command basis. In
addition, a slave status list is maintained per active
Modbus Master port.
1 to 247 (software selectable)
Error codes, counters and port status available per
configured slave port
Reference
User Manual
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