User manual

Rockwell Automation Publication MOTION-UM003F-EN-P - March 2015 193
Home an Axis Chapter 8
• A power loss
• A download of an axis that does not have its home bit set
• Power cycling of an incremental encoder
Behavior of APR for Incremental Encoders
APR for incremental encoders means Absolute Machine Reference Position
Retention. When an incremental encoder is homed, the homed bit is set.
When any of the events and/or conditions that generate an APR fault for an
absolute encoder occur for an incremental encoder then an APR fault is
generated and the axis home bit is cleared.
For example, the behavior of APR faults for an incremental encoder is identical to
that of an absolute encoder except when an incremental encoder is power cycled,
and its position comes up as 0. Its Absolute Machine Reference Position is lost.
An APR fault is not generated.
TIP
When you perform an import/export on a project in the RSLogix 5000
software, version 19 or earlier, the axis absolute position is not
recovered on download to the controller.
The APR can potentially be restored from a CompactFlash card on a
1756-L6x or 1756-L6xS controller (if a battery is not present) or an SD
card on a 1756-L7x controller (if a 1756-ESMxxx module is not
present) as described on page 182
.