ProSoft Technology MVI46-MCM - Manual (Page 74)

Reference MVI46-MCM ♦ SLC Platform
User Manual Modbus Communication Module
Page 74 of 108 ProSoft Technology, Inc.
March 29, 2011
Master Driver Mode
In the Master mode, the MVI46-MCM module issues read or write commands to
slave devices on the MODBUS network. These commands are user-configured
in the module via the Master Command List received from the SLC processor or
issued directly from the SLC processor (Event Commands or Command Control).
Command status is returned to the processor for each individual command in the
command list status block. The location of this status block in the module’s
internal database is user-defined. The following flow chart and associated table
describe the flow of data in and out of the module.
Step Description
1 The Master driver obtains configuration data from the SLC processor. The configuration
data obtained includes the number of commands and the Master Command List. These
values are used by the Master driver to determine the type of commands to be issued
to the other nodes on the Modbus network (Refer to the Module Set Up section).
2 After configuration, the Master driver begins transmitting read and/or write commands
to the other nodes on the network. If writing data to another node, the data for the write
command is obtained from the module’s internal database to build the command.
3 Presuming successful processing by the node specified in the command, a response
message is received into the Master driver for processing.
4 Data received from the node on the network is passed into the module’s internal
database and the M1 file, assuming a read command.
5 Status is returned to the SLC processor for each command in the Master Command
List.