Browse Prior Art Database

Display Stroke Random Positioning Calculations

IP.com Disclosure Number: IPCOM000048833D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Bowen, RA: AUTHOR

Abstract

In a vector stroke type of display, the cathode ray tube (CRT) deflection coils require different periods for their deflection currents to build up between the display of consecutive characters, depending upon the separation distance between those characters on the display face. In the past, a maximum deflection current build-up time was assumed for each intercharacter display period. Since all of the vector strokes must be generated before the CRT phosphors decay, it becomes increasingly difficult to display large quantities of information.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 57% of the total text.

Page 1 of 3

Display Stroke Random Positioning Calculations

In a vector stroke type of display, the cathode ray tube (CRT) deflection coils require different periods for their deflection currents to build up between the display of consecutive characters, depending upon the separation distance between those characters on the display face. In the past, a maximum deflection current build-up time was assumed for each intercharacter display period. Since all of the vector strokes must be generated before the CRT phosphors decay, it becomes increasingly difficult to display large quantities of information.

This problem is solved by the display stroke random positioning circuit disclosed herein, which accurately estimates the duration for deflection current build-up in the deflection coils, based upon the larger value of either the X component of the separation distance or the Y component of the separation distance between the consecutive characters to be displayed.

The beam repositioning time is calculated and defined as the greater of the following two equations. P(T) Equals I(c) Plus X(1) Minus X(o)

P(T) Equals I(c) Plus Y(1) Minus Y(o) where P(T) Equal positioning time I(c) Equals initial minimal beam movement time for

positioning, constant

X(o) Equals new X position

X(1) Equals present X position

Y(o) Equal new Y position

Y(1) Equal present Y position

I(c) is a time constant for initial beam movement for any positioning; the additional time is then a linear correlation from the maximum X or Y movement.

This calculation then determines the exact beam repositioning time so that the video output for the next character can be turned on as soon as the beam has been accurately repositioned. This maximizes the amount of graphic data which can be displayed.

The refresh control circuit shown in the figure will accurately determine the repositioning time of the CRT beam necessary before drawing the next character or vector. The beam is positioned by loading a new X and Y position into the X and Y counters for each graphic symbol. The counters are then changed by incremental values through the drawing of the graphic symbol.

For each new graphic symbol on the CRT screen the CRT beam must be repositioned to a new location. This hardware then calculates the time for that repositioning.

The following calculation example is taken from the programmable display generator. X(1) Equals 403 decimal

Y(1) Equals 172 decimal

X(o) Equals 121 decimal

1

Page 2 of 3

Y(o) Equals 194 decimal

The beam...