Each CCD frame begins with a CCD Frame Header, which contains an ID code, housekeeping data, and information on the events found within that frame. The housekeeping data stored in the CCD Frame header includes values of the 50 general HK channels (1--50) and the 25 HK channels for the CCD being read out (51--75 for CCD1 or 76--100 for CCD2). The same frame header is used for normal frames (with event recognition) and for compressed frames (without event recognition), but the Frame Header ID word for the latter is different so that the ground processing software can identify compressed frames and decode the data in them correctly. Bit assignments for the CCD Frame Header are given in Table 35. Complete details of the Frame Header formats are provided in the CUBIC Flight Software Reference.
Table 35: CUBIC CCD Frame Header
Each CCD Frame Header begins with a fixed 32 bit ID word, followed by a 16 bit frame counter, CCD number (8 bits), the total number of events in the frame, the number of single events in the frame, and the number of split events (all 16 bits). This provides 11 bytes of frame ID and checks for recognition of the beginning of a CCD frame header, since the frame number should increment sequentially, the CCD number can only have one of two possible values, and the sum of the single and split events should equal the total event number. This should provide unambiguous CCD frame identification for extraction from the data stream. In addition to the embedded 16 bit Synch Words, compressed CCD frames also include a row counter for each CCD row to ensure synchronization.
The format of the CUBIC CCD data in RAM is shown in Table 36.
Table 36: CUBIC Science RAM Data Format