home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
LOGIC Apps
/
Logic-APPLE_II_APPS.iso
/
mac
/
LOGIC Apple II 5.25" Library - ProDOS
/
PRO079B.dsk
/
IIC
/
IIC.02.GRAPHICS.txt
< prev
next >
Wrap
Text File
|
2012-02-16
|
4KB
|
69 lines
Apple II
Technical Notes
_____________________________________________________________________________
Developer Technical Support
Apple IIc
#2: 40-Column and Double High-Resolution Graphics
Revised by: Matt Deatherage November 1988
Revised by: Cameron Birse February 1986
This Technical Note describes how to properly handle the 40-column screen
while using double high-resolution graphics on the Apple IIc.
_____________________________________________________________________________
Many developers using double high-resolution graphics may wish to use 40-
column text displays so that the text can be read on a television set. There
are a couple of possibilities for accomplishing this task:
1. You can define your own double high-resolution character set with
any size characters you desire, then plot them on the double high-
resolution screen.
2. You can print text to the Apple IIc text screen and toggle the
screen on to display it.
Note: There is no way to display 4 lines of 40-column text at the
bottom of the double high-resolution screen in mixed mode since
the 80 column hardware must be active while double high-resolution
mode is being used.
Using the second method outlined above requires some special considerations.
The Apple IIc scroll routine continues to use the window parameters when
scrolling, but uses the 80COL softswitch to determine if it should scroll the
80-column screen or 40-column screen. Since the firmware has initialized a
40-column window, the scroll routines will move only the first 40 columns, but
the 80COL flag has been turned on for double high-resolution. Because of the
80COL flag, the scroll routine takes every even column from auxiliary memory
and every odd column from main memory. As a result, only the first 40 columns
get scrolled, 20 columns from auxiliary memory and 20 columns from main
memory.
One solution to the problem is writing your own scroll routines, while another
is writing to the screen so scrolling is not necessary. There is, however,
another solution. Turn on the full 80-column mode with PR#3 or equivalent.
Now print your text to COUT in the normal manner, and do not exceed 40
characters per line--the 80-column firmware should scroll everything properly.
When you are ready to display text, send a Control-Q sequence through COUT to
toggle to 40-columns and send a Control-R sequence to return to double high-
resolution mode. These control characters toggle the display modes, but leave
the 80-column firmware active.
When switching between modes, you may experience a momentary glitch. If you
send the Control-Q sequence to COUT while still in graphics mode, the screen
will first switch to the normal high-resolution mode before finally switching
to text mode. If you switch to text mode first, the text will be in 80-column
mode (with 40 columns displayed on the left of the screen) before ultimately
switching to 40-column mode). This same potential glitch may occur when
switching back to double high-resolution mode, and it may be only momentary
and not present any problems for your application. If, however, it does
present a problem, you may wish to make your switch coincide with the video's
vertical blanking interval (see the Apple IIc Technical Reference Manual).
Further Reference
o Apple IIc Technical Reference Manual