Epson PX-8 User Manual page 36

2.2.6 The Screen of the PX-8
When you view the LCD screen of the PX-S, you are looking at a window on
a much larger screen. The screen displayed on the LCD is known as the real
screen. This is S lines high by SO columns. The operating system works with
a much larger screen, a screen of up to 40 lines and SO columns. The real screen
then displays a window on this larger screen (the virtual screen), which is called
the virtual screen window.
Virtual screen window
Real sc reen
Function key display area (optional)
There are also four different screen modes (including a graphics mode) which
show different types of display. In all but the graphics mode there are two vir-
tual screens.
This section outlines the different screen modes and shows how to use them.
Changing between different screen modes can be achieved using the CONFIG
program described in Chapter 3.
It
is also possible to change the screen modes
using BASIC commands, and the BASIC Reference Manual contains a practi-
cal guide to the screen modes in section 2.14.
It is unlikely that you will use the different screen modes in the CP 1M environ-
ment unless a particular applications program has made use of them. However,
there are certain benefits to be obtained by learning to use the tracking and
non-tracking modes, and to understand the virtual screens. As these would be
utilised mainly in screen mode 0, a detailed explanation is given in the follow-
ing outline of this screen mode.
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i)
The Screen Modes
There are four screen modes possible with PX-S. Three of them are text only
screens, and the fourth is a mixed text and graphics mode. The difference be-
tween the modes is primarily the way the real screen presents the information
written on the virtual screens.
a) Screen mode 0 (the 80 column text screen mode)
This screen mode has two virtual screens each with SO columns. The number
lines on these screens can be set by the user provided that the sum of the num-
ber of lines does not exceed 4S and there are at least S lines (i.e. one real screen-
ful of lines) on each screen.
n1
Virtual Screen 1
1 - - - -
80 columns -----0-1
r
n2 lines
Virtual Screen 2
+ - - - - - 8 0 columns - - -......
0011
1.L..-----...J
Conditions: n 1 2: 8
n22:8
h=7 or 8
n1 +n2;::;;48
The virtual screen window moves over the virtual screen to display a part of
the virtual screen on the real screen. This movement is known as scrolling. When
the real screen moves over the virtual screen, scrolling with the cursor, this is
known as tracking mode. Tracking mode can be switched off by pressing the
I
SCRN
I
key
(I
SHIFT
1+ I
INS
I).
When this is done the cursor moves over the
virtual screen while the real screen stays at the same place on the virtual screen.
The real screen becomes locked in a particular position on the virtual screen.
The following illustration will show the effect of scrolling in the tracking and
non-tracking modes.
It
assumes that the virtual screen size of 24 lines on each
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