ProSoft Technology MVI56E-MNET/MNETXT - Manual (Page 110)

Reference MVI56E-MNET / MNETXT ♦ ControlLogix Platform
User Manual Modbus TCP/IP Interface Module
Page 110 of 181 ProSoft Technology, Inc.
April 23, 2014
5.2 Backplane Data Transfer
The MVI56E-MNET module communicates directly over the ControlLogix
backplane. Data is paged between the module and the ControlLogix processor
across the backplane using the module's input and output images. The update
frequency of the images is determined by the scheduled scan rate defined by the
user for the module and the communication load on the module. Typical update
times range from 1 to 10 milliseconds.
This bi-directional transfer of data is accomplished by the module putting data in
the input image to send to the processor. Data in the input image is placed in the
processor's controller tags by ladder logic. The input image is set to 250 words.
Processor logic inserts data to the output image to be transferred to the module.
The module's firmware program extracts the data and places it in the module's
internal database. The output image is set to 248 words.
The following illustration shows the data transfer method used to move data
between the ControlLogix processor, the MVI56E-MNET module and the Modbus
TCP/IP Network.
All data transferred between the module and the processor over the backplane is
through the input and output images. Ladder logic must be written in the
ControlLogix processor to interface the input and output image data with data
contained in the controller tags. All data used by the module is stored in its
internal database. This database is defined as a virtual Modbus data table with
addresses from 0 (40001 Modbus) to 4999 (45000 Modbus).