The Si1120 has seven operating modes that range from measuring the ambient light to the reflected IR as well as determining the output LED drive current from the TXO pin. PRX400 is best for range, PRX50 is best for power saving (PRX50H is not generally used). OFC mode is typically used to figure out the minimum PRX pulse width without an LED which is representative of the PRX pulse width during dark ambient conditions since the LED is not turned on. OFC is used more rarely than either PRX400 or PRX50 as it is more like a calibration step and probably is done once every time the system boots and the value is stored in memory. OFC is used to represent what the PRX50 or PRX400 would have reported if there was no reflected IR energy. The PRX400 minus the OFC value, for example, is a more accurate representation of the reflectance. In applications implementing ambient light sensing, VAMB, VIRL and VIRH will all be used equally. However, not all applications will require ambient light sensing.