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FOT LAYOUT: MHER7/MHTR4/MHTR5



This information should be read in conjunction with the descriptions of these OBC modes given in
EXOSAT Express No.12 and p.36.

MHER7

Program 72.

11 workspace parameters.

wsp 2 = distance between consecutive samples in units of 2-14 seconds.

wsp 3 = number of samples per bin of intensity profile.

wsp 4/5 = start/end channels of 1st or only energy range.

wsp 6/7 = start/end channels of 2nd range; both zero if only one range.

wsp 8/9/ = limits of 3rd and 4th ranges; all are zero, if there 10/11 are I or 2 ranges only.

Record type on FOT = 17.

MHTR4

Program 73.

4 workspace parameters.

wsp 2 = as for HER7

wsp 3/4 = start/end channel of selected energy range.

Record type on FOT = T4.

MHTR5

Program 74.

2 workspace parameters.

wsp 2 = as for HER7, but note that the QE is sampled, not the energy.

Record type on FOT = T5.

General information for all 3 Programs

A All three programs produce records similar in layout to ME/MHTR3, namely:

bytes 0-3 = reference time
bytes 31 = unused
bytes 32-287 = 256 bytes of actual data



For MHER7, the data samples are 4 bits long and are stored such that the time increases more rapidly than the energy range. One record thus contains data for all the (1, 2 or 4) selected ranges. For MHTR4 the samples are 1 bit long, ie. the value 1 indicates that an event within the selected energy range occurred. For MHTR5 the samples are again 4 bits long. The value 15 for a four bit counter means "greater than or equal to 15".


In all cases information is stored to tape in chronological order of its reception on the ground, which means (for users of HP and IBM computers) in order of decreasing significance within a memory buffer. This applies at the bit level as well as the byte level. Users of DEC computers must take special care that samples are accessed in the correct order, because their address convention at the byte level differs from the convention used in OBC and FOT documentation. Within a byte, the "decreasing significance" convention applies to all computers, eg. the first sample of an MHTR4 record should be extracted from the most significant bit of a byte.



J.R. Sternberg


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