There are basically two references available: Vss and AGND. The voltage value of AGND is user selectable through the RefMux settings in global resources window in PSoC Designer. The exact value can be found in the device datasheet for any particular setting. The operating ranges are as follows:
1. Vss reference: The input can be Vss to Vdd, however, since the op-amp is not rail to rail, the output operating range can be found in the respected user module datasheet.
2. AGND reference: The operating range is between RefLo and RefHi. The values of RefLo and RefHi can be found in the device datasheet for various Ref Mux settings in the global resources window in designer.