Browse Prior Art Database

CRT Font Storage Control

IP.com Disclosure Number: IPCOM000035112D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 4 page(s) / 64K

Publishing Venue

IBM

Related People

Ashbee, WH: AUTHOR [+3]

Abstract

Disclosed is a method to properly display "reverse video" characters on a CRT screen with minimum character font storage.

This text was extracted from a PDF file.
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CRT Font Storage Control

Disclosed is a method to properly display "reverse video" characters on a CRT screen with minimum character font storage.

In Fig. 1, CRT characters are displayed using bright dots (pels) on the face of the screen. The character matrix (1B,2B) is smaller than the character box, and is 16-pels x 16-pels. The character itself is formed within the character matrix. The remaining pels within the character box that are not part of the character matrix become blanks.

A problem exists if the character matrix is positioned at the top of character box (1). In this case, if the character is displayed in "reverse video," the pels in the top raster line of the character become blank, and blend into the blank raster of the character in the row above it. The character matrix must be positioned within the character box so that at least one blank raster line is present in both the top and bottom raster lines of the character matrix (2).

An obvious solution is to provide sufficient storage space to store all pel information contained within the character box. This would require 40 bytes of storage per character, five (5) address lines and would consume 64 bytes of address space.

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This article describes a means to resolve the display problem while, at the same time, minimize storage space.

Since the character in question is 16-pels x 16-pels, the actual storage space required is 32 bytes. Four raster address bits are required to scan 16 lines. Thus there is no wasted space within storage.

In Fig. 2, video display controller (3) generates the necessary control and address lines to control the CRT. To properly address font storage, there are two groups of addresses: 1....