Rockwell Automation 1336T Function Block Prog. Manual, Series A/B - Manual (Page 61)

3–13 System Interactions
1336 FORCE — 5.9 August 1995
A drive with a connected PLC Communication Board has two link
processing mechanisms. One link processing mechanism operates
specifically upon linear parameter links, and the other mechanism
processes the function block links.
As the application executes, the function block links are processed
block by block. The inputs for each individual block are checked for
links. If a link is found, the link processor goes to the source
parameter or node and copies the data from the source to the
destination node. Once all data for the links to one function block is
gathered, the function block algorithm is executed. The system can
then begin processing the next function block. Because the function
block application is executed every 20 milliseconds, the data for an
individual link is also updated every 20 milliseconds.
Currently, the link mechanism for the linear parameters executes
every 1 to 2 milliseconds. This updates all of the linear parameter
links (up to the maximum of 50) every 1 to 2 milliseconds.
Therefore, two function block nodes that receive input from the same
linear parameter may receive different data values within the same
task interval.
For example, if you have an application with 115 events that takes 12
milliseconds to execute and the input for event 1 and event 115 are
linked to the feedback, event 115 may receive a value that is
different than the value event 1 received during the same execution
task interval pass.
LIMIT
MULTIPLY
Feedback
from the drive
Input
Input
Event 1
Event 115
L1
L2
In this example, L1 represents the first transfer of data, which occurs
when Event 1 is processed. L2 represents the second transfer of data,
which occurs when Event 115 is processed. The data transferred in
L1 and L2 may have different values.
Performance Issues Involving
Links