ProSoft Technology MVI46-MBP - Manual (Page 53)

Reference MVI46-MBP ♦ SLC Platform
Modbus Plus Communication Module
ProSoft Technology, Inc. Page 53 of 101
February 19, 2008
Master Driver Mode
In the Master mode, the MVI46-MBP module issues read or write commands to
other devices on the Modbus Plus network. These commands are user-
configured in the module via the Master Command List received from the SLC
processor or using the command control blocks. Command status is returned to
the processor for each individual command in the command list status block. The
module emulates the MSTR Type 1 and Type 2 commands in terms of data read
and write functionality. The following flow chart and associated table describe the
flow of data into and out of the module.
Master
Mode
Driver
MBP Memory
Configuration
Master
Command List
Status
3
1
2
4
5
0
3999
4000
4369
4370
7089
40001
44000
44001
44370
44371
47090
Modbus
Addresses
Database
Addresses
User Data
Files
Status
Configuration Configuration
Data
Status
from Module
Register
Data
storage
Register
Data
Processor Memory Backplane Interface
Event Cmd
Data
7170
7182
47171
47183
Event Cmd
Data
Event Cmd
Data
Command
Queue
M0 File Command
Control
6
Step Description
1 The Master driver obtains configuration data from the SLC processor. The configuration
data obtained includes the number of commands, the Device Definition File, and the
Master Command List. These values are used by the Master driver to determine the type
of commands to issue to the other nodes on the Modbus Plus network. In addition, Event
Command control bits are available to control individual commands from ladder logic.
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 other nodes, responses are received into the
Master driver for processing.
4 Data received from the other nodes on the network is passed into the module's internal
database, assuming a read command.
5 Status is returned to the SLC processor for each command in the Master Command List.
6 Ladder logic can alter the enable code for commands or cause the master driver to
execute user commands or commands in the list by placing the commands in the
command queue.
In order for the MVI46-MBP module to operate in the Master Mode (actively
reading/writing data with other nodes on the network), several user configurable
parameters must be received from the SLC processor. The following topics detail
these configuration requirements.