A typical absolute encoder will output a 10 or 12 bit wide bit pattern in either true binary or gray code, if your system only accepts quadrature, then these cannot be used.
Some systems however use a method of battery back up of the quadrature signal, but again, this is system dependant.
If you go to a web site like BEI that offer absolute encoders, they should have a detailed explanation.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.