Browse Prior Art Database

Light Pen Operation

IP.com Disclosure Number: IPCOM000086950D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Davies, AR: AUTHOR [+2]

Abstract

In a raster display, a light pen is used to interact with the screen. The operator places the light pen against the screen and operates a switch. This causes the display system to determine where the pen is placed on the screen. To operate the light pen needs light so that if it is pointed to a nonilluminated part of the screen, special provisions must be made.

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Light Pen Operation

In a raster display, a light pen is used to interact with the screen. The operator places the light pen against the screen and operates a switch. This causes the display system to determine where the pen is placed on the screen. To operate the light pen needs light so that if it is pointed to a nonilluminated part of the screen, special provisions must be made.

Current display systems use a "raster blast" technique which operates as follows: The light pen is placed against the screen at the required point and the tip switch is operated. The system illuminates a matrix of points to ensure light pen detection. The finer the resolution required, the larger the number of illuminated points. In the limit, every displayable point is illuminated. To minimize visual shock on the operator, it is normal to use a partial raster blast. Thus, to prevent visual shock some sacrifice of resolution is made. In addition, data on the screen is obscured or obliterated, at least, momentarily.

These shortcomings can be overcome by using the following technique. The light pen is placed against the screen and the tip switch is operated. This will happen at some random time in the refresh cycle, referred to as cycle 0. In the next refresh cycle, that is cycle 1, the display is refreshed normally and the system attempts to locate a positive light pen detect. If detection occurs, the pen must be in an illuminated area and the system can take appropriate action in the normal way. If, on the other hand, no detection occurs in cycle 1, the system examines a "raster blast enable" bit which would normally be on bu...