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Typewriter Display of Proportionally-Spaced Characters

IP.com Disclosure Number: IPCOM000039743D
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Clark, RE: AUTHOR [+4]

Abstract

Proportionally-spaced characters are displayed on an all-points-addressable (APA) display in exactly the way that they are to be printed on a sheet of paper. The display of the proportionally-spaced characters uses printer control information for proportional-spaced character placement, underscore length, and cursor control. Proportionally-spaced characters are displayed on an APA display, such as a cathode ray tube, by passing a character code, which allows selection of the correct character font data, and a printer carrier position, which is the actual position of the carrier of the typewriter, to a Display Control processor. Using the printer carrier position, the Display Control processor calculates a base character position and an offset from that position for the specific proportionally-spaced character.

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Typewriter Display of Proportionally-Spaced Characters

Proportionally-spaced characters are displayed on an all-points-addressable (APA) display in exactly the way that they are to be printed on a sheet of paper. The display of the proportionally-spaced characters uses printer control information for proportional-spaced character placement, underscore length, and cursor control. Proportionally-spaced characters are displayed on an APA display, such as a cathode ray tube, by passing a character code, which allows selection of the correct character font data, and a printer carrier position, which is the actual position of the carrier of the typewriter, to a Display Control processor. Using the printer carrier position, the Display Control processor calculates a base character position and an offset from that position for the specific proportionally- spaced character. The video random- access memory (RAM) write routine within the Display Control processor shifts the font data to the right of the base character position the offset amount to position the character for display before writing it to the video RAM. The same process is used to erase a proportionally- spaced character from the screen as when the character is displayed. However, '0's are substituted for '1's in the data read from the font and written to the video RAM. Since the length of an underscore of a proportionally-spaced character is dependent on the width of the character, the escapement value of the...