MVI69L-MBS ♦ Platform
Reference
Modbus Serial Lite Communication Module
User Manual
ProSoft Technology, Inc.
Page 89 of 130
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 MVI69L-MBS can work as a Master and as a Slave.
The MVI69L-MBS also works as an input/output module between itself and the
Rockwell Automation backplane and CompactLogix 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 30 commands on the
port. The Master port has an optimized polling characteristic that polls slaves with
communication problems less frequently.
Command List
Up to 30 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.
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
processor.
Node address
1 to 247 (software selectable)
Status Data
Error codes, counters and port status available per configured
slave port
