User manual

Reference MVI56-HART ♦ ControlLogix Platform
User Manual HART Multi-drop Master Communication Module
Page 84 of 171 ProSoft Technology, Inc.
October 13, 2011
5.2.2 Backplane Data Transfer
The MVI56-HART module communicates directly over the ControlLogix backplane. Data
travels between the module and the ControlLogix processor across the backplane using
the module's input and output images. The update frequency of the data is determined by
the 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.
Data received by the master drivers is placed in the module's input image. This data is
processed by the ladder logic in the ControlLogix processor. The input image for the
module is set to 500 bytes. This large data area permits fast throughput of data between
the module and the processor.
The processor inserts data in the module's output image to transfer to the module. The
module's program extracts the data and transmits the data out to the master driver to the
serial network. Additionally, the ControlLogix processor can send special control blocks to
the module to instruct it to perform a special task. The output image for the module is set
to 496 bytes. This large data area permits fast throughput of data from the processor to
the module.
The following illustration shows the data transfer method used to move data between the
ControlLogix processor, the MVI56-HART module, and the HART networks.
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 ControlLogix processor
to interface the input and output image data defined in the controller tags. The user is
responsible for handling and interpreting all data received on the application ports and
transferred to the input image.
As blocks are transferred between the module and the processor, each block contains
block identification codes that define the content or function of the block of data
transferred.