Rockwell Automation 1756-XXXX ControlLogix Digital I/O Modules - Manual (Page 87)

Rockwell Automation Publication 1756-UM058G-EN-P - November 2012 87
Fast Module Features Chapter 5
Per Point Timestamping and Change of State
With per point timestamping, each input point on the module records
timestamps in CIP Sync format at these speeds:
• ± 4 μs for inputs < 4 kHz
• ± 13 μs for inputs > 4 kHz
You can configure an input point to record a timestamp when the point
transitions from On to Off, Off to On, or in both directions. By default, all
points are configured to record a timestamp in both directions.
You can also configure the module to latch timestamps for an input point’s last
transition. When latching is enabled for a specific point, the point records a
timestamp in the Pt[
x].Timestamp.OffOn or Pt[x].Timestamp.OnOff input
tags. The timestamp remains latched, and no new timestamps are recorded for
the input point until the timestamp is acknowledged and reset. As a result, you
can use the timestamp to determine the speed of a transition that is too fast to be
detected by the program scan.
To acknowledge a transition and reset a timestamp latch, you set the
corresponding bit in these output tags:
• Pt[
x].NewDataOffOnAck—Acknowledges that the input point has
transitioned to an On state and resets the timestamp latch.
• Pt[ x].NewDataOnOffAck—Acknowledges that the input point has
transitioned to an Off state and resets the timestamp latch.
The Pt[
x].TimestampDropped input tag indicates whether a new timestamp has
not been recorded because a previous timestamp was either latched or
unacknowledged.
Once a timestamp latch is reset for an input point, a new timestamp may be
recorded in the Pt[
x].Timestamp.OffOn or Pt[x].Timestamp.OnOff input tags
upon the next transition.
You can configure per point timestamping in three ways:
• Timestamping enabled without latching (default configuration)
• Timestamping enabled with latching
• Timestamping disabled
IMPORTANT Timestamping functions only in a CIP Sync system. If you are using change of
state (COS) in a system using Coordinated System Time (CST), all timestamp
values and the GrandMasterClockID input tag are set to zero.
To set up CIP Sync time synchronization on the local controller, use the
Date/Time tab in the controller properties. For more information about CIP
Sync configuration, refer to the Integrated Architecture and CIP Sync
Configuration Application Technique, publication IA-AT003 .