User`s guide

Parameters
The external encoder device type is 0. This means that the type parameter in all DEVICE or
SETDEVICE instructions that reference the external encoders must have a value of zero.
The standard Adept controller allows two external encoder units. These units are numbered
0 and 1. All DEVICE functions and SETDEVICE instructions that reference the external
encoders must specify one of these unit numbers for the unit parameter.
Parameters
V+Language User's Guide, v17.0
Page 352