Rockwell Automation 1756-XXXX ControlLogix Digital I/O Modules User Manual
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Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Appendix C
Use Ladder Logic To Perform Run Time Services and Reconfiguration
The only difference is the output module is configured for scheduled
outputs. The outputs will not get applied until the scheduled time has
occurred.
The Controller Tags dialog box below shows examples of the tags created
in ladder logic.
Use Timestamped Inputs and Scheduled Outputs for Fast I/O Modules
This section demonstrates the use of timestamped inputs and scheduled outputs
for fast digital I/O modules. The Change of State timestamp can be used to
synchronize the output turning On or Off based on the time that the input
transitions. The program can be extended to include synchronizing multiple
output modules by sending the same timestamp to all output modules.
In the example below, the output follows the state of input 0, but it is delayed by
the amount of time in the Delay tag. The advantage of using CIP Sync over
timers is that the synchronization is performed at the I/O module, which
eliminates any jitter due to controller or communication delays.
Your control becomes much more deterministic even under changing loads. For
this synchronization to work properly, the value in the Delay tag must be long
enough to account for any controller, backplane, and network delays.
In this example, the controller, input, and output modules all reside in the same
chassis, but they can reside in separate chassis as long as they are all part of the
same synchronized CIP Sync system. Timestamp units are microseconds.
IMPORTANT
Unlike standard and diagnostic I/O modules that use CST for timestamps,
fast I/O modules use CIP Sync timestamps, which are a full 64 bits in width.
Manipulation of CIP Sync time values requires the use of 64-bit math. The
following example uses 64-bit Add-on Instructions contained in the LINT
(64-bit signed 2's complement integer) Math Library located at
.