Backplane Data Transfer - ProSoft Technology MVI69-DFCM User Manual

Functional Overview

2.1.3 Backplane Data Transfer

The MVI69-DFCM module is unique in the way that the CompactLogix backplane is
utilized. 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. You can configure the size of the blocks using the Block Transfer Size parameter
in the configuration file. You can configure blocks of 60, 120, or 240 words of data
depending on the number of words allowed for your own application.
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, 122, or 242 words depending on the block transfer size parameter set in the
configuration file.
The processor inserts data to the module's output image to be transferred 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 diagram displays the data transfer method used to move data between the
CompactLogix processor, the MVI69-DFCM module and the DF1 network.
Processor Processor
Processor Processor
Controller Tags Controller Tags
Or User Files Or User Files
Status Status
Read Data Read Data
Write Data Write Data
Special Control Special Control
Blocks Blocks
As shown in the diagram above, 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 input and output image data
4
Ladder Ladder
Logic Logic
Transfers Transfers
Data from Data from
Input Image Input Image
module's input module's input
image to data image to data
areas in the areas in the
processor processor
Ladder Ladder
Logic Logic
Transfers Transfers
Data from Data from Output Image Output Image
Processor Processor
data areas data areas
to output image to output image
MVI69-DFCM Module MVI69-DFCM Module
Module's Module's
Internal Internal
Database Database
Master Master Master
Driver Driver Driver
Logic Logic Logic
Slave Slave Slave
Driver Driver Driver
Logic Logic Logic
ProSoft Technology, Inc.
MVI69-DFCM User Manual
DF1 DF1
Port Port
Drivers Drivers
To DF1 To DF1
Network Network
June 24, 2004