Level 0 Data
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[edit] CAVEAT
The data are reversed from the ElOp presentations because they read the bytes in reverse order. The format in this document is as would be read by a binary dump of the data.
The transmission direction from the TAUVEX instrument has to be confirmed at the bit level.
[edit] Data format
The TAUVEX data consist of 1024 bit major frames with each frame beginning with 64 bits of hexadecimal data: B0 95 28 27 C7 76 47 03. Following this sync word is 960 bits of data. The minor frame is further subdivided into 24 segments of 40 bits each.
Each data file is nominally a single observation and will begin with and end with a Log file. This should be distinguished from the data file received from the MCF (Master Control Facility) in Hassan which nominally contains data from spacecraft noon to noon.
[edit] Filler
These data include the filler data added on board to maintain a constant data rate of 1 Mbps. The filler is a series of 01 with the last two bits of the first byte being 00. Thus one segment will be 0100 0101 0101 0101 0100 0101 0101 0101 0101 0101 or A8 AA AA AA AA
No major frame (1024 bits) will contain both filler and data; rather a frame will be either filler or data but not both.
Each observation will begin with at least 195 major frames of filler.
[edit] Log Data
There are two event logs: the START LOG at the beginning of the observation and the END LOG at the finish. The START LOG contains all the commands relating to TAUVEX between the end of the previous observation and the start of the current one while the END LOG consists of all commands relating to TAUVEX during the obsrvation.
The LOG data are distinguished by having the last two bits of each segment being 10. The format of the LOG tables is contained in the Appendix.
The Log data will begin after a sync word and should start with FF FF FF FF 01 FF FF FF FF 01 FF
[edit] Science Data
The science data will also be in the form of major frames with the only difference being that the last two bits of each segment being 10. Because the science data may not fill the 1 Mbps data stream, the data are padded with filler containing only 01. Data and filler will not be mixed in a major frame; that is, a frame will only contain data if there are enough data to fill the entire frame. Thus the last data frame may be discarded if there are not enough data to fill the frame.
The last two bits of each data segment will be 10 and the first 2 will be:
00 for time tag 01 for telescope #1 02 for telescope #2 03 for telescope #3
In the case of time tag data, the last 20 bits of each segment will be the time in units of 128 ms where the MSB is bit 20 and LSB is bit 1. The telescope data always consists of 36 bits with w, s, and z being 12 bits each. If the TAUVEX mode is CLBR, w0, s0, and z0 will be read instead. If we define:
W = w - w0 S = S - s0 Z = z - z0
then
x = W/(W + S + Z)*2048 - x0 y = S/(W + S + Z)*2048 - y0
assuming a pixelization of 1024 x 1024.
