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Light Pen Register Utilization for Diagnostic Purposes

IP.com Disclosure Number: IPCOM000049928D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Freeman, JW: AUTHOR [+2]

Abstract

A cathode ray tube (CRT) attachment controls the refreshing of a raster scan display in the following manner: A read-only store (ROS) contains the dot patterns of all characters which may be displayed. A character buffer within main storage contains one location for each unique character X-Y coordinate position on the display. When a character is to be refreshed, the corresponding character buffer location will contain the address of the proper character dot pattern in the ROS. The CRT attachment computes the character X-Y coordinate position according to the location's relative position within the character buffer.

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Light Pen Register Utilization for Diagnostic Purposes

A cathode ray tube (CRT) attachment controls the refreshing of a raster scan display in the following manner: A read-only store (ROS) contains the dot patterns of all characters which may be displayed. A character buffer within main storage contains one location for each unique character X-Y coordinate position on the display. When a character is to be refreshed, the corresponding character buffer location will contain the address of the proper character dot pattern in the ROS. The CRT attachment computes the character X-Y coordinate position according to the location's relative position within the character buffer.

The CRT attachment's light pen register may be used to verify proper operation of the CRT attachment. A special character is loaded into a known location in the character buffer. This special character has the attribute that when displayed, its X-Y coordinates are loaded into the X-Y coordinate locations of the light pen register which is part of the attachment. When the location containing the special character is reached by the attachment, it computes the character coordinate position and loads these character coordinates into the light pen register. The character coordinates as stored in the light pen register may be compared to the known character coordinates to assure that the attachment is properly addressing the character buffer and properly computing display X-Y coordinate positions.

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