Author: Rilla Reynolds
Year: 1987
... discusses a 280 x 192 monochrome high-resolution mode available on the Apple IIGS.
Apple II
Technical Notes
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Developer Technical Support
Apple IIGS
#29: Monochrome High-Resolution Mode
Revised by: Rilla Reynolds November 1988
Written by: Rilla Reynolds October 1987
This Technical Note discusses a 280 x 192 monochrome high-resolution mode
available on the Apple IIGS and useful for clarifying some graphics.
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You can select a 280 x 192 monochrome high-resolution mode on the Apple IIGS
with the following steps:
1. Select Monochrome and 40-column from the Control Panel (which sets
the 40-column soft switch and bit 5 in $C029).
2. Select Hi-Res graphics mode (which sets GR and HIRES soft
switches).
3. Read from to write to $C05E (AN3).
To deselect the mode, read from or write to $C05F.
A monochrome double high-resolution mode also exists on the IIGS, and you
follow the same procedure outlined above to access it.
You can use the monochrome mode to display sharper graphics-mode text and fine
lines for applications which do not require color. Note that Applesoft BASIC
also supports the monochrome video mode.
The soft switches you must access in software to enable the monochrome high-
resolution mode are as follows:
GR $C050
HIRES $C057
40COL $C00C (for monochrome double hi-res, use 80COL at $C00D)
AN3 OFF $C05E
In addition, you must set bit 5 of the register at $C029, and you must use a
read-modify-write sequence since $C029 is a multi-function register.
You can manipulate all of the soft switches listed above from the IIGS
Monitor, except 40COL.