Rockwell Automation 8520-ARM2 9/Series CNC AMP Reference Manual Documentation Set - Manual (Page 209)

Servo Parameters
Chapter 7
7-63
Digital systems must use the motor--mounted feedback device (that comes
preinstalled on the 8500 and 1326 digital motors) for velocity feedback.
This encoder/resolver can not be removed from the motor or realigned with
the motor shaft. This device is used for motor commutation.
This parameter tells the control the type of velocity feedback device used
for the axis (typically the same feedback device selected with the
parameter Position Feedback Type). These options are:
No Feedback -- only selected if the velocity loop is closed by an
external device (typically the drive for analog systems). This option is
not valid for digital systems. Digital motors must always close the
velocity loop through the CNC with the encoder/resolver device
attached directly to the motor shaft.
ABS Encoder on Dig. Mod. -- for axes using an absolute encoder for
velocity feedback. If Allen-Bradley 8500 Series standard digital motors
are used with absolute encoders, this setting must be selected as the
velocity feedback type.
Important: Absolute encoders are not compatible with the analog servo
interface or 9/440 resolver based systems. 9/440HR systems only
support the 1326 motor--mounted High--resolution Absolute encoders
option. You should not select the “ABS Encoder on Dig. Mod”
feedback type when configuring an analog servo interface or 9/440.
INC Encoder U/V/W on Dig. Mod. -- for axes using an incremental
encoder for velocity feedback.
U/V/W refers to the special feedback channels in this encoder necessary
for initial commutation of the motor. If Allen-Bradley standard 8520 or
1326 digital motors are used and they have incremental encoders, this
must be selected as the velocity feedback type. This selection is also
used when connecting to the 1394 CNC system module or the 9/440.
The 1394 system module and 9/440 convert the resolver signals from
the 1326 motors into encoder signals for commutation.
Analog system can also use these encoders. However, the U, V, and W
channels cannot be connected. The A, B, and Z channels for the
encoder are handled the same way as a normal incremental encoder with
a narrow marker (Z < A).
INC Encoder A/B/Z (Z < A) -- for axes that have a narrow marker
differential incremental encoder (sometimes called a “gated” encoder).
Z < A refers to a narrow marker pulse. This means that there is only
one period during which the A, B and Z channels can simultaneously be
high. Select this feedback type if using Allen-Bradley bulletin 845H
encoders. Refer to page 7-50 Figure 7.29 for examples.
Digital systems cannot use this selection.