Browse Prior Art Database

Vertical Scrolling

IP.com Disclosure Number: IPCOM000045505D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Rosenbaum, F: AUTHOR

Abstract

Current cathode ray tube (CRT) terminals scroll data one line at a time. That is, Line 1 is replaced by Line 2, Line 2 is replaced by Line 3, etc., and the last line is replaced by the new line added to the screen. The problem with this method is the data cannot be read as the display is scrolling. If the characters were to move up the screen smoothly like credits on a movie screen, the information could be read.

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Vertical Scrolling

Current cathode ray tube (CRT) terminals scroll data one line at a time. That is, Line 1 is replaced by Line 2, Line 2 is replaced by Line 3, etc., and the last line is replaced by the new line added to the screen. The problem with this method is the data cannot be read as the display is scrolling. If the characters were to move up the screen smoothly like credits on a movie screen, the information could be read.

This is not done on any existing terminal because only line scrolling is supported. Line scrolling is accomplished simply by changing the start address of the display buffer. This causes the entire screen to jump up one row.

The function of a cathode ray tube controller (CRTC) is to constantly refresh the CRT screen. This is accomplished by sweeping the CRT beam across the screen, displaying dots, one row at a time, to build a character. Each character consists of several scan lines. Commonly available character generators provide anywhere from 7 to 15 scan lines per character (Fig. 1).

To refresh the screen, the CRTC will read the first character from the screen buffer and present it to the character generator, along with a zero on the character generator row address input. The character generator will then output the dot pattern for that character. This is fed to a shift register and shifted out to the video processing logic. This continues for the entire scan line. For the next scan line, the same data is read, but a 1 is presented to the character generator row address input. This sequence is repeated (7 to 15 times), incrementing the row address each time. The same events happen for the following rows, but different data is addressed (Fig. 2) for a representation of several characters. Fig. 3 shows character generator contents for a "T" and "+".

Current CRTCs offer scrolling only by changing the start address for the screen buffer. This causes the entire display to jump one data row. To offer smooth scrolling, or rolling, requires that the characters move up one scan line at a time. In other words, instead of the first character row starting with character generator row address 0, it would start with 1. The last line of the screen would then display row address 0 of the new line. To continue scrolling, the first row would start with character generator row 2, and the bottom would display character generator row 0 and 1, and so on, until the entire first line was off the screen and the entire new line was displayed on the bottom. The process would be repeated to scroll another data row.

Of course, the data displayed in between the top and bottom rows would move up only one scan line at a time also, and the data could be read while scrolling. This allows an operator to constantly scroll and read data, as opposed to adding a few lines to the bottom, then stopping to read what has been added.

The processor (not shown), through either an output command or writing to a memory-mapped data latch, clears La...