Master Mode - ProSoft Technology CompactLogix MVI69E-MBS User Manual

MVI69E-MBS ♦ CompactLogix™ Platform
Modbus Serial Enhanced Communication Module

5.4.2 Master Mode

In Master mode, the MVI69E-MBS module issues read or write commands to slave
devices on the Modbus network. These commands are user-configured in PCB; refer to
Modbus Port x Commands (page 44). This list is transferred to the module when the
module receives its configuration from the processor.
The commands can also be issued directly from the CompactLogix or MicroLogix 1500-
LRP processor (Special Command Blocks).
Command status is returned to the processor for each individual command in the
command list. The location of this command status list in the module's internal database
is user-defined. The following flow chart and associated table describe the flow of
command data into and out of the module.
Description
Step
Upon module boot-up, the Master driver obtains configuration data from the MBS
1
controller tags. The configuration data retrieved includes port configuration and the
Master Command List.
Special Commands can be issued directly from the CompactLogix or MicroLogix 1500-
LRP processor using Event Commands and Command Control. These command values
are used by the Master driver to determine the types and order of commands to send to
slaves on the network.
After configuration, the Master driver begins transmitting read and/or write commands to
2
slave nodes on the network. If the Master driver is writing data to a slave, the data for the
write command is retrieved from the module's internal database.
Once the specified slave has successfully processed the command, it returns a response
3
message to the Master driver for processing.
Data received from a slave in response to a read command is stored in the module's
4
internal database.
Status is returned to the processor for each command in the Master Command List.
5
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