The energy values of the events provided in the telemetry are given as a bin number from 0 to 255. These are non-linear groupings of the original 4096 bins of the on-board Analog to Digital Converter (ADC). While the ADC channels are highly linear, the PHA bins are designed to be logarithmic so that the energy resolution of the bins parallels that of the detector. The actual grouping of the ADC channels into PHA telemetry bins is determined by a lookup table used by the Data Processing Electronics (DPE) to pack the telemetry. After the high voltage reductions this table has been updated to match the changed ADC signal strengths.
See also Appendix B.3 for more details.