Browse Prior Art Database

Horizontal Smooth Scrolling for a CRT Display

IP.com Disclosure Number: IPCOM000047103D
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 77K

Publishing Venue

IBM

Related People

Leppala, RA: AUTHOR [+2]

Abstract

Rows of dot-matrix characters on a cathode-ray tube (CRT) display are moved dot-by-dot to the right or left by using a variable-width cycle before the display of each scan during successive video frames. In Fig. 1, prebox register 1 is loaded with the desired width (number of dots) of the first character of the current row. The contents of this register control the horizontal width of the first character; this in turn controls the horizontal screen position of the remaining characters of the entire row. The update rate and time of register 1 determines which portions of the screen are to scroll, and at what rates. Width counter 2 counts down the number of horizontal dots for each character cycle. It can be selectively loaded with either the normal box width or the prebox width.

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Horizontal Smooth Scrolling for a CRT Display

Rows of dot-matrix characters on a cathode-ray tube (CRT) display are moved dot-by-dot to the right or left by using a variable-width cycle before the display of each scan during successive video frames. In Fig. 1, prebox register 1 is loaded with the desired width (number of dots) of the first character of the current row. The contents of this register control the horizontal width of the first character; this in turn controls the horizontal screen position of the remaining characters of the entire row. The update rate and time of register 1 determines which portions of the screen are to scroll, and at what rates. Width counter 2 counts down the number of horizontal dots for each character cycle. It can be selectively loaded with either the normal box width or the prebox width. Decoder 3 translates the counter contents into various timing and sequencing signals. During the first cycle of each character row, counter 2 is loaded from prebox register 1. If the prebox width is normal, the row timing is not displaced, and its appearance is normal. As register 1 is loaded with other values, the first cycle (prebox cycle) varies, causing the timing and sequencing signals to be displaced, as shown in Fig. 2. Periodically updating register 1 causes the character row to move smoothly across the screen. Row buffers 4, character generator 5, and serializer shift register 6 are of any type conventionally used with raster-scanned d...