ProSoft Technology MVI69-DNP - Manual (Page 73)

Reference MVI69-DNP ♦ CompactLogix or MicroLogix Platform
DNP 3.0 Master/Slave Communication Module
ProSoft Technology, Inc. Page 73 of 129
November 3, 2008
Backplane Data Transfer
The MVI69-DNP module communicates directly over the CompactLogix or
MicroLogix 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
defined by the user for the module and the communication load on the module.
Typical updates are in the range of 2 to 10 milliseconds.
The data is paged between the processor and the module using input and output
image blocks.
This bi-directional transference of data 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 words.
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 words.
The following illustration shows the data transfer method used to move data
between the CompactLogix processor, the MVI69-DNP module and the DNP
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
CompactLogix processor to interface the block data with user data files. All data
used by the module is stored in its internal database. The following illustration
shows the layout of the database: