ProSoft Technology MVI69E-MBTCP - Manual (Page 64)

MVI69E-MBTCP Backplane Data Exchange MVI69E-MBTCP ♦ CompactLogix Platform
User Manual Modbus TCP/IP Enhanced Communication Module
Page 64 of 150 ProSoft Technology, Inc.
May 20, 2015
4.2 Backplane Data Transfer
The MVI69E-MBTCP module communicates directly over the CompactLogix
backplane. Data is paged between the module and the CompactLogix 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 that you
define for the module and the communication load on the module. Typical
updates are in the range of 1 to 10 milliseconds per block of information.
This bi-directional data transfer is accomplished by the module filling in data in
the module's input image to send to the processor. Data in the input image is
placed in the Controller Tags in the processor by the ladder logic. The input
image for the module may be set to 62, 122, or 242 words depending on the
block transfer size parameter set in the configuration file. This data area permits
fast throughput of data between the module and the processor.
The processor inserts data to the module's output image to transfer to the
module. The module's program extracts the data and places it in the module's
internal database. The output image for the module may be set to 61, 121, or 241
words depending on the block transfer size parameter set in the configuration
file.
The following illustration shows the data transfer method used to move data
between the CompactLogix processor, the MVI69E-MBTCP module and the
Modbus Network.
All data transferred between the module and the processor over the backplane is
through the input and output images. Ladder logic in the CompactLogix
processor interfaces the input and output image data with data defined in the
Controller Tags. All data used by the module is stored in its internal database.
This database is defined as virtual MBTCP data tables with addresses from 0 to
the maximum number of points for each data type.