ProSoft Technology MVI56E-MCMR - Manual (Page 170)

Reference MVI56E-MCMR ♦ ControlLogix Platform
User Manual Modbus Communication Module with Reduced Data Block
Page 170 of 225 ProSoft Technology, Inc.
May 13, 2014
6.3.5 Slave Driver
The Slave Driver Mode allows the MVI56E-MCMR module to respond to data
read and write commands issued by a remote Master on the Modbus network.
The following flow chart and associated table describe the flow of data into and
out of the module.
1 The Modbus Slave port driver receives the configuration information from the
Compact Flash Disk. This information configures the backplane exchanges,
user memory Read and Write Data areas, the serial ports, and Modbus Slave
Device characteristics. Additionally, the configuration information contains
parameters that can be used to offset data in the database to addresses
different from those requested in messages received from Master units.
2 A Remote Master Device, such as a Modicon PLC or an HMI application,
issues a read or write command to the module’s Modbus Slave Device
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 out of 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 3, the response is
issued to the originating Master Device.
5 Counters are available in the General Module Status (page 153) Block that
permit the ladder logic program to determine the level of activity of the Slave
Driver.
Refer to Configuration as a Modbus Slave (page 81) for a list of the parameters
that must be defined for a Slave port.