SIXA has six different observing modes which can be selected by the observer: three different SEC (single event characterization) modes, Energy-Spectrum Mode (ESM), Window-Counting Mode (WCM), and Time-Interval Mode (TIM). The control over the modes is shared between two processors, so that one DPU (SEC DPU) runs the SEC modes, and the other DPU (EGY DPU) the three other modes. The ESM, WCM and TIM can be run in parallel with one SEC mode (maximum of four modes simultaneously), and any of the modes can be switched off independently. The starting and ending times of each spectrum are stored with a 10 ms timing accuracy. The time resolution in SEC, ESM and WCM is about 30.5 microseconds, and in TIM it is 12.21 microseconds.
The storage capacity of SIXA is 44Mbytes between observing sessions. For the Crab Nebula, the count rate is 6000 cts s-1 which will fully fill the 44Mbyte memory in 3 hours (in raster scan mode). For the Perseus cluster with a count rate of 2.4, 1.4, and 0.5 cts s-1in the central element, 6 inner circle elements, and 12 outer circle elements respectively, the data will consume 6Mbytes of memory (4Mbytes for EGY spectra and 2Mbytes for SEC data).