Cyclic Read and Cyclic Write
Cyclic data is real time information, sent and received between the controller and the integrated motion drive at the Coarse Update Period. If you want to make use of cyclic data you must use the Axis tag to access the data, thus provide data at the motion group's Coarse Update Period.
TIP:
Cyclic write attributes are unique in that they have attribute storage policed by the object handler (either Logix Designer or GSV/SSV) and also have direct tag access which bypass the object validation.
The value written into the tag is validated before being written to the drive and that if that validation fails you will see an 'out of range alarm' and flag it in the axis fault/alarm log but that the value in the tag remains as written by the user. The value of the internal attribute as viewed using GSV or in Logix Designer shows the previously validated value.
The following is an example of configuration and rung reference using the following five Cyclic Read/Write Drive Parameters.
Three Read Parameters
- Velocity Error
- Motor Electrical Angle
- DC Bus Voltage
Two Write Parameters
- Acceleration Feedforward Gain
- Velocity Loop Bandwidth
The attributes to be accessed as Cyclic Read/Write are configured for the CIP Axis on the Drive Parameters page and accessed through the Axis_tag.backing_structure_attribute.
When you are online, the Cyclic Drive Parameters list is condensed to show only the selected parameters when the Servo Loop=Enabled. When the Servo-Loop=Off, then all parameters in both the Read & Write list are shown on the page. Additionally the parameters populated in the list are filtered based on the Axis Configuration: P, V, T, N, F.
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