The SPI on-board electronics is in charge of the real time acquisition, assembly, time stampling and intermediate storage of the various pieces of information coming from the detectors, the PSD and the ACS. Events are subdivided into classes depending on their origin in the instrument (detector electronics, detectors, PSD, veto shield) and are further used to monitor the system statistics (dead time, signal counts etc.). The detected events are time tagged with a 20 MHz local clock, which provides the timing resolution. The reset (timing reference) is done with the 8 Hz satellite clock.