ProSoft Technology MVI69E-MBS - Manual (Page 70)

MVI69E-MBS Backplane Data Exchange MVI69E-MBS ♦ CompactLogix Platform
User Manual Communication Module
Page 70 of 162 ProSoft Technology, Inc.
January 6, 2014
4.1 General Concepts of the MVI69E-MBS Data Transfer
The MVI69E-MBS module uses ladder logic to communicate with the
CompactLogix processor across the backplane. The ladder logic handles the
module data transfer, configuration data transfer, special block handling, and
status data receipt.
The following topics describe several concepts that are important for
understanding the operation of the MVI69E-MBS module.
1. On power up the module begins the following logical functions:
- Initialize hardware components
- Initialize CompactLogix backplane driver
- Test and clear all RAM
2. Read configuration from the CompactLogix processor via ladder logic
3. Allocate and initialize Module Register space
4. Enable Modbus application ports
5. After the module has received the Module Configuration, the module
begins communicating with other nodes on the Modbus network,
depending on the Modbus configuration of the module.
4.2 Backplane Data Transfer
The MVI69E-MBS 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.