Rockwell Automation 1756-SYNCH ControlLogix SynchLink Module User Manual - Manual (Page 42)

Publication 1756-UM521C-EN-P - July 2004
3-14 SynchLink Module Features
Buffered, Direct and Diagnostic Data - RPI Effect on Input Data (to the
controller)
The RPI is one of two mechanisms available through the 1756-SYNCH
module to update the module’s input data onto the backplane. Input
data is transferred from the SynchLink module to its owner-controller
at the rate defined in the RPI.
In addition to the RPI, Change of State (COS) functionality also causes
the module to produce its data to the consuming controller whenever
the values of the data changes. The RPI timer is asynchronous to the
COS functionality. Both cause the module to produce data when
triggered.
Buffered, Direct and Diagnostic Data - RPI Effect on Output Data (from the
controller)
As a producing controller writes data to the 1756-SYNCH module, the
output data is placed in a local buffer until the next RPI reset occurs.
When the RPI timer expires, the output data is moved from the
controller’s local buffer to the 1756-SYNCH module.
The RPI timer is asynchronous to the program execution. Therefore, a
worst case update to the SynchLink module can be calculated by
adding the program execution time to the RPI timer setting, as
configured by the user.
The SynchLink module minimum RPI = 2.0mS. The RPI is configured
on the following screen:
Requested Packet Interval