4 axis quadrature encoders?
I just found this (TMS320x2833x, 2823x Enhanced Quadrature Encoder Pulse (eQEP) Module from TI). Probably not the same component that you use, but similar functionality.


  eQEPI: Index or Zero Marker
  The eQEP encoder uses an index signal to assign an absolute start position from which position
  information is incrementally encoded using quadrature pulses. This pin is connected to the index
  output of the eQEP encoder to optionally reset the position counter for each revolution. This signal can
  be used to initialize or latch the position counter on the occurrence of a desired event on the index pin.
  
  QEPS: Strobe Input
  This general-purpose strobe signal can initialize or latch the position counter on the occurrence of a
  desired event on the strobe pin. This signal is typically connected to a sensor or limit switch to notify
  that the motor has reached a defined position.