Rockwell Automation 1746-HSCE,D17466.5 High-Speed Counter Module - Manual (Page 164)

Publication 1746-UM006B-EN-P - August
C-2 Differential Encoder Information
5. Since the encoder may be mounted on either end of a motor
shaft, the encoder may spin CW or CCW for a given shaft
direction. As a result, the direction (phasing) of the encoder may
be backwards. If this is the case, switch the Channel A wires
with the Channel B wires. This changes the direction of the
encoder signals. The wire at A(+) exchanges with wire at B(+).
The wire at A(-) exchanges with wire at B(-).