International Business Machines Corporation

Paul R Herrold

William C Cason, Jr

Ward A Kuecker

Douglas A Hamilton

Multiple virtual images are built on a display screen of a text processing system by a display access method (DAM) program running interrupt identified service programs. Each of the service programs is provided with stack memory elements for retaining data to run the program. Each of the service programs is run by the DAM program in accordance with priority interrupts with a higher priority interrupt having immediate access to the DAM program. A service program having a low priority interrupt that is being run by the DAM program will be stopped by the occurrence of a higher priority interrupt with the data and address information of the interrupted program retained in the stack memory elements. The service program of the higher priority interrupt is then run and when ended the DAM program retrieves the data for the lower priority program to return to the point of interruption. This program of the lower priority interrupt is then run to an end if not again interrupted by a higher priority interrupt.

Single screen display system with multiple virtual display having

A cathode ray tube display system is provided for displaying alphanumeric characters which are cyclically refreshed in the sequence of selected positions. The system has conventional means for moving the CRT beam through an arbitrary sequence of selected positions with reference to first and second coordinate axes, in response to position signals, and character defining means for deflecting the beam at each selected position within which a selected character may be defined and in response to signal representations of said selected character for modulating the beam intensity along said pattern to define the character. The system further includes storage means for sequentially storing a coded representation of the character selected to be displayed as well as tab codes and carriage return codes for said displayed characters. In addition, the means for generating said position signals include: (1) means responsive to an access tab code for calculating the tab position for the next character to be displayed with respect to the first coordinate axes only in the initial cycle during which each of the selected characters is formed, (2) means for storing each of these calculated tab positions, and (3) means operable only during refresh cycle responsive to a tab code for accessing the stored previously calculated tab position corresponding to said code.

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Austin, TX, United States of America

Paul R Herrold