EP0139095A2
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EP
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Display selection in a raster scan display system
Assignee: International Business Machines Corp
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Filing: 1984-07-05
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Granted: —
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Expires: 2004-07-05
Abstract
Abstract In a raster scan digital display system, a display image is stored, as coded characters or a bit map, which is larger than the display image. In order to define an image, within the stored image, for display, the addressing system for the memory (or memories) storing the image include a display image defining circuit. This circuit includes an address counter which is incremented to define successive addresses of data in a line of the displayed image, or row of characters therein. The circuit includes a first register to receive the initial address of a display image and a second register to receive a value indicating the width of the stored image. For the initial line (or character row) of a displayed image, the address counter is loaded from the first register and incremented from the initial address. For each subsequent line (or character row) the address from which the counter is incremented is the sum of the initial address of the previous line (or character row) and the value in the second register.
Inventors
- 👤 David Allen Kummer
- 👤 Jesus Andres Saenz
- 👤 Stephen Wayne Trynosky
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-24 21:45
CPC Classifications
G; G06; G06F; G06F3/00; G06F3/14; G06F3/153; G09; G09G; G09G5/00; G09G5/36; G09G5/39; G09G5/395; G09G5/34; G09G5/343; G09G5/346
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
245 words
A raster scan display system including a memory (MAPO-MAP3) for storing data for display on a raster scan display device, said memory storing a logical data image (20) larger than a physical data image (21) displayable on the display device, and means (8,9,10) for addressing the memory to access data representing a physical data image from the stored logical data image, characterised in that said addressing means comprises a first register (31) for storing the initial address of a stored physical data image, a second register (30) for storing a data value representing the number of addresses of horizontal elements of the physical data image, means (32) selectively operable to direct the content of the first register or the output of an adder (36) to a third register (33), means (43) coupling the output of the third register to a first input of the adder and to an address counter (35), means (38) coupling the output of the second register to a second input of the adder and control means (in 8) effective to cause transfer of data from the first register to the address counter via the selectively operable means and third register at the start of scanning of a displayed physical image, to increment the address counter during each scan line and to reload the address counter from the output of the adder via the selectively operable means and third register at selected horizontal retrace times during scanning of said displayed physical image.
Claim 2
Dependent Claim
245 words
A raster scan display system including a memory (MAPO-MAP3) for storing data for display on a raster scan display device, said memory storing a logical data image (20) larger than a physical data image (21) displayable on the display device, and means (8,9,10) for addressing the memory to access data representing a physical data image from the stored logical data image, characterised in that said addressing means comprises a first register (31) for storing the initial address of a stored physical data image, a second register (30) for storing a data value representing the number of addresses of horizontal elements of the physical data image, means (32) selectively operable to direct the content of the first register or the output of an adder (36) to a third register (33), means (43) coupling the output of the third register to a first input of the adder and to an address counter (35), means (38) coupling the output of the second register to a second input of the adder and control means (in 8) effective to cause transfer of data from the first register to the address counter via the selectively operable means and third register at the start of scanning of a displayed physical image, to increment the address counter during each scan line and to reload the address counter from the output of the adder via the selectively operable means and third register at selected horizontal retrace times during scanning of said displayed physical image.
Claim 3
Dependent Claim
55 words
A raster scan display system as claimed in claim 1 in which the selectively operable means is responsive to a vertical scan retrace signal to transfer the output of the first adder to the third register and to the absence of this retrace signal to transfer the output of the adder to the third register.
Claim 4
Dependent Claim
106 words
A raster scan display system as claimed in claim 2 including a logic circuit (34) coupled to receive said vertical scan retrace signal and a signal indicating the end of scanning of a selected row of the displayed image and having an output coupled to the third register to control the same, the selectively operable means (32) being coupled to receive the vertical retrace signal, the combination being effective to load the address counter and adder with its content in response to a row end signal and no vertical retrace signal and with the content of the first register in response to the vertical retrace signal.
Claim 5
Dependent Claim
34 words
A raster scan display system as claimed in any preceding claim, operable in the bit mapped mode, in which the selected horizontal retrace times are each retrace time during scanning of the displayed image.
Claim 6
Dependent Claim
55 words
A raster scan display system as claimed in any preceding claim, operable in character generation mode, in which said memory contains character codes by which a display character pattern memory is accessed and in which the selected horizontal retrace times are each retrace time which immediately follows the scanning of a displayed row of characters.
References Cited (Backward Citations)
No citation records indexed.
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