Viewports; Visual Effects Of Screen And Page Lengths - Boundless ADDS 3153 LF ASCII Manual To Operations

Display terminal

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Viewports

Up to three viewports can be selected on a page. Each viewport has its own character attribute, cursor

position, field attribute propagation, tab stops and scrolling region. All of the viewports are displayed on the

same screen and can be partitioned with a visual separator line. If the keyboard is associated with one viewport

and the host is associated with another, it is possible to receive data in two viewports simultaneously. The figure

below represents the entire page memory of a 48 line page (24 base page length times a multiplier of 2) and the

portion of the page that is viewable on the display screen, when "26 Lines" is selected. Notice that the label line

is visible in this mode.

The combination of page and screen lengths influence the number of displayable data lines. For example, if the

page length is "50" (25 x 2), and the screen length is 44 lines, the number of data lines that are visible at any

one time is 43, with no label line. The other line is used for the top status line. On a 52 line screen, 50 of the 52

data lines are visible at one time.

If the page length is shorter than the screen length, then blank lines will be present below the data line or

status/label line. If the page length is larger than the allowable number of data lines, this will cause some of the

rows to be out of view. In order to bring them into view, "scrolling" or "panning" is used, as necessary. Scrolling

causes a new line to scroll into view when the cursor advances past the last row or first row on the page. If the

page is scrolled down, the top row of text is lost, and if scrolled up, the bottom row of text is lost (if Auto Scroll is

"on" in Setup). Text scrolled off of the screen is not recoverable.

If the current page or portion of the page is longer than the screen display or window in which it is displayed,

then local keystrokes can be used to "pan" the window up or down (Ctrl-ì and Ctrl-Å ). As a window is panned

up, the page appears to be moving down and the opposite is true when panning the window down. Text that is

panned off the screen is out of view, but is not lost.

The figure below represents the display screen with a 48 line page length on a 44 line screen, after panning the

window down 2 lines.

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