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40 Rockwell Automation Publication 1756-RM100F-EN-P - October 2018
Chapter 2 Replacement Considerations with ControlLogix 5580 and GuardLogix 5580 Systems
Communication Throughput
Unlike 5570 controllers, which shares the main core between application code
and communications, 5580 controllers run communications asynchronously
from the user application.
This implementation provides better communications throughput in both the
bandwidth and speed of data the 5580 controllers can deliver to and from, for
example, HMIs, Historians, and MES systems. It also improves the overall
application performance as the controller no longer has to task switch and
pause application execution to handle HMI or other class 3 traffic.
For 5570 and 5580 controllers, the controller runs communication
asynchronously to the application, make sure communication that is delivered
to the controller is complete before the application executes on the newly
delivered data. This applies to both data that comes into the controller and
data that goes out.
For example, if the HMI is writing a large block of recipe data to the controller,
application code can start executing on that recipe data before the data writing
process finishes. This action results in half of the current recipe and half of the
last recipe in the application space.
Traditionally, programmers have used the following techniques to control the
effects of asynchronous communications:
• UID/UIE pairs
• Periodic tasks
• Moving data with CPS instructions
The techniques all rely on controlling when the main core can switch tasks.
This helps to prevent the communications task from changing data while the
control task used it. Because the controller processes communications on an
independent core of the CPU, then UID/UIE pairs and Periodic Tasks are not
as effective in all cases.
The items that are highlighted in this table are where controller behavior
differs.
Table 7 - ControlLogix 5570 and ControlLogix 5580 Controller Behavior Differences
Tag Read/Write
Source UID/UIE CPS Periodic Task
5580 Controllers 5570 Controllers 5580 Controllers 5570 Controllers 5580 Controllers 5570 Controllers
HMI Allows Blocks Blocks Blocks Allows Blocks
MSG Allows Blocks Blocks Blocks Allows Blocks
I/O Update Allows Allows Blocks Blocks Allows Allows
Produce/Consume Allows Allows Blocks Blocks Allows Allows
Other User Tasks Blocks Blocks Blocks Blocks Allows Allows
Motion Planner Allows Allows Blocks Blocks Allows Allows
Blocks - Stops source data values from change by communications during application execution.
Allows - Communications can change source data values during application execution.