ProSoft Technology MVI69L-MBS - Manual (Page 68)

MVI69L-MBS Backplane Data Exchange MVI69L-MBS ♦ CompactLogix Platform
User Manual Communication Module
Page 68 of 154 ProSoft Technology, Inc.
January 6, 2014
4.1 General Concepts of the MVI69L-MBS Data Transfer
Ladder logic is required for the MVI69L-MBS module 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.
For most applications, the sample Add-On Instruction (which includes the ladder
logic) works without modification.
The following topics describe several concepts that are important for
understanding the operation of the MVI69L-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 port
5. After the module has received the Module Configuration, the module
begins communicating with other nodes on the Modbus network,
depending on the configuration
4.2 Backplane Data Transfer
The MVI69L-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 defined by the
user 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 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 is 242 words. This data area permits fast throughput
of data between the module and the processor.