Backplane Data Transfer - ProSoft Technology MVI69-DFCM User Manual

Compactlogix platform df1 interface module
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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

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