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RXTE Cook Book: DDL, SEFILTER, and Event Mode Data
Recipes from the RXTE Cook Book

This is a general recipe discussing PCA event mode data, the data descriptor language (DDL), and the tool sefilter. All of this information can be found in the technical appendix (Appendix F), the XFF Documents, the fhelp, other recipes, or the ABC Guide and is summarized here in a more compact and perhaps clearer form.

In science event data, all of the information is encoded in the individual bits of the event word. Different event modes encode the information in different ways expressed using the Data Descriptor Language (DDL; see the ABC Guide). This recipe summarizes common examples and how to use them.

The first thing that is important to realize is that, since the data are stored as a series of bits, a "bit-mask" must be developed which is appropriate for the file that is being processed. This bit-mask is of the form "Column name, relational operators, Bit-mask" (e.g. Event == b1xxxxxxxxxxxxxxx, with the "bit-mask" being denoted from other types of values by the presence of a "b" in front of the bit-mask.) You do not need to make this expression yourself; the script sefilter will make it for you if you know what values you want in different parts of the event word. It will give you a token expressed in the DDL and ask you for a value. It will then construct an expression in the DDL which is passed to sebitmask which actually constructs the bitmask. Sefilter then gives you options for using the bitmask depending on its form. Neither the extractor nor fselect is capable of determining if a bitmask is sensible, however, so you need to understand the DDL in order to be sure you get what you intend.

  • A note on strategy:

    You can use the information in both the TEVTB2 and TDDES2 keywords to figure out the best way to filter your data. If the TEVTB2 says E[0:63]{6} and the TDDES2 says E[X1L^X1R^X2L^X2R^X3L^X3R], the anode information is there but only non-coincidence events are included in the file, so no values but powers of two would appear in the file. To ask for E[0:63]==24 in sefilter would be perfectly valid, but would result in an empty file. The advantage of this is in simplicity. Say you wanted layers one and two, corresponding to values 1,2,4, and 8. If you have a file with coincidence events, you will have to specify these values by entering "1,2,4,8" at the sefilter prompt. It will then form an OR expression, which cannot be used by seextrct. If, however, the file contains no intermediate values, you can simply say "1-8", forming a simple AND expression, and you'll get the right result in seextrct, bypassing the lengthy fselect process.

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    This page is maintained by the RXTE GOF and was last modified on Friday, 16-May-2008 14:08:34 EDT.