For an incremental encoder, after an axis successfully executes its homing sequence the home position by definition establishes the zero position for the encoder.  This offset is added to the home zero position to allow the encoder zero position and the joint zero joint position to be arbitrarily shifted relative to the home position.

For an absolute encoder, after the encoder value is read during the homing operation, this offset is added to the encoder reading.  This offset permits the absolute encoder value to be shifted to adjust for any difference between its zero position and that of the axis.

For the Precise Absolute Encoder, these two values (the index code and the absolute position at the index) are used by the run-time homing process to convert a valid index code into its corresponding absolute position. If the index code is 0, then the position data is ignored and the run-time calibration will fail.  Normally, these values are determined during a factory calibration setup procedure.

When the method for refining motor commutation angles using zero index signals is enabled, each motor's "Commutation position, mcnt" (12651) is set to the value specified by this parameter the first time an incremental encoder's zero index is detected.  Since a zero index signal typically occurs at a fixed commutation angle, this method permits the commutation position to be set very accurately and can correct any errors that occurred during the reference finding method.  For example, this avoids any errors due to gravity or friction that may have affected the results of the commutation reference finding method.

This value of this parameter can range from -1 to the value defined by "Commutation counts per electrical cycle, mcnt" (10652).

To enable this feature, this parameter must be set to a value greater than -1 and the bit field 4:6 of the "Commutation reference setup config" (10700) must be set to 0.