ProSoft Technology MVI56E-MCM/MCMXT - Manual (Page 135)

MVI56E-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 135 of 199
June 18, 2014
Slave Driver
The Slave Driver Mode allows the module to respond to data read and write
commands issued by a Master on the Modbus network. The following illustration
describes the flow of data to and from the module.
1 The Modbus Slave Port driver receives the configuration information from the
ControlLogix processor. This information configures the serial port and
defines the Slave node characteristics. Additionally, the configuration
information contains data that can be used to offset data in the database to
addresses requested in messages received from Master units.
2 A Host device, such as a Modicon PLC or an HMI application, issues a read
or write command to the module’s node address. The port driver qualifies the
message before accepting it into the module.
3 After the module accepts the command, the data is immediately transferred
to or from the internal database in the module. If the command is a read
command, the data is read from the database and a response message is
built. If the command is a write command, the data is written directly into the
database and a response message is built.
4 After the data processing has been completed in Step 2, the response is
issued to the originating Master node.
5 Counters are available in the Status Block that permit the ladder logic
program to determine the level of activity of the Slave Driver.
Refer to Using the Sample Program in an Existing Application (page 186) for a
complete list of the parameters that must be defined for a Slave Port.