Browse Prior Art Database

CRT Raster Dot Character Generation

IP.com Disclosure Number: IPCOM000087464D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 83K

Publishing Venue

IBM

Related People

Kuhar, E: AUTHOR

Abstract

A technique is described for generating raster dot characters suitable for commercial quality television (TV) monitor displays. It provides relatively adequate character quality on TV monitors, using a lower fundamental video output write rate, thus reducing bandwidth requirements. This technique allows up to 80 characters per line, using available digital switching logic circuits. Circuits are provided to generate 8 (horizontal) by 7 (vertical) video dot matrix characters. Its features are: (1) the application of a video pulse to the unblanking circuit during 2 succeeding video dot matrix intervals (i.e., T1 corresponds to 2 video dot intervals and T1, T2, T3, T4 correspond to the 8 row dots of a character) and (2) the overlapping of signals TA-TC with T1-T4).

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CRT Raster Dot Character Generation

A technique is described for generating raster dot characters suitable for commercial quality television (TV) monitor displays. It provides relatively adequate character quality on TV monitors, using a lower fundamental video output write rate, thus reducing bandwidth requirements. This technique allows up to 80 characters per line, using available digital switching logic circuits. Circuits are provided to generate 8 (horizontal) by 7 (vertical) video dot matrix characters. Its features are: (1) the application of a video pulse to the unblanking circuit during 2 succeeding video dot matrix intervals (i.e., T1 corresponds to 2 video dot intervals and T1, T2, T3, T4 correspond to the 8 row dots of a character) and (2) the overlapping of signals TA-TC with T1-T4). These features result in sharper character images and permit a larger number of characters per line in a standard low-cost cathode-ray tube (CRT) display.

Fig. 1 illustrates several individual characters, each having an 8-bit code sequence underneath. This 8-bit sequence is actually an EBCDIC character representation that is different for each character and that is provided to the random-access memory 1 (Fig. 2) on the data line from an associated processor or a keyboard. The random-access memory has sufficient capacity to store 24 rows of 80 characters each, that is, 1920 total characters comprising the entire face of the CRT and mainly required for "refresh" purposes, that is, to insure character brightness. Each of the 1920 addressable storage locations stores an individual 8-bit representation of the EBCDIC character to be reproduced in the corresponding display character matrix position. These locations are addressed by an 11-bit address pattern. Six bits of each of the EBCDIC character representations are combined with 3 bits from a row counter thus totaling 9 bits used to address 512 l...