By Juergen Kopf* and Dirk Abeln;
Institut fuer Anorganische und Angewandte Chemie der Universitaet Hamburg, Martin-Luther-King-Pl. 6, D-20146 Hamburg, Germany.
Two years ago we reported on ''The Application of Graphic Desktop Software in Single Crystal Diffractometry'' (Abeln, D. and Kopf, J., Abstract PS-02.06.01 IUCr XVI, Beijing, China, 1993). In this report we presented a new diffractometer control program for a 24 years old Hilger & Watts (Y290) rebuild with four stepper motors. The design goal was to provide a user interface which is easy to learn and to give a novice user the ability to collect data effectively while giving the experienced user all the control necessary to complete difficult tasks. A further goal was to make the program easily portable for different instruments and different computers. Therefore, the software including system software for GEM-calls is completely written in FORTRAN77 and much attention was paid that the structure of the program is modular (Abeln, D. PhD Thesis, University of Hamburg, 1995).

By isolating all modifications required to drive a different instrument, it was possible in between three weeks to re-write the same control program for an 18 years old, mechanically still reliable SYNTEX P21 diffractometer. This instrument was one of the first diffractometers where the control software was completely written in FORTRAN. The computer used at that time was the (now obsolete) Data General NOVA. Later this computer was replaced by a new ''SIEMENS-interface'' which simulates the Nova 1200. In contrast to the old-fashioned, 2-letter command structure given on a VT100 the new control program uses easy to learn drop-down menus, dialog-, alert- and file-selector-boxes. The availability of the source code allowed the easy implementation of crystal-based Psi-angles (Schwarzenbach, D. and Flack, H. D., J. Appl. Cryst., 1989, 22, 601) for numerical absorption corrections with the program ABSPSI (Alcock, N. W. and Marks, P. J., J. Appl. Cryst., 1994, 27, 200) and SHELXL93.

Although an ATARI Mega ST2 with 1 Mbyte memory and only 8 MHz processor speed is completely sufficient even to continously display on-line profiles of all scan-types for each reflection, a PC version (Linux/X11) is under development.

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Last changed: 16-Nov-2001. Jürgen Kopf