MVI69E-MBS ♦ CompactLogix™ Platform
MVI69E-MBS Backplane Data Exchange
Modbus Serial Enhanced Communication Module
User Manual
ProSoft Technology, Inc.
Page 67 of 159
5.2
Backplane Data Transfer
The MVI69E-MBS module communicates directly over the CompactLogix or MicroLogix
1500-LRP backplane. Data is paged between the module and the CompactLogix or
MicroLogix 1500-LRP 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. Applications that require smaller amounts of data or faster update
times, such as ControlNet networks, will benefit from smaller block transfer sizes.
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 or MicroLogix 1500-LRP processor, the MVI69E-MBS module and the
Modbus Network.