SPC8106 S-MOS Systems, SPC8106 Datasheet - Page 211

• Manufacturer Part Number: SPC8106
• Description: LCD/CRT VGA CONTROLLER
• Manufacturer: S-MOS Systems

0.0.0.2 Graphics Modes
As with text modes, the horizontal display will be clipped. But, for panels less than 400 lines, we
have modified the modes which normally double 200 lines to 400 scan lines back to an undoubled
200, so that vertically they will display correctly. For modes that are a full 480 scan lines, the BIOS
cannot undouble the mode, so the will be clipped in the vertical direction.
Software Compatibility
A major concern when modifying standard mode values (including font and offset information) is
the software that does not compensate for these changes. Most text mode software expects a
standard VGA font to be present (16 pixel high) and may not expect this to change. Programs that
modify the text cursor, or program their own font probably will not work correctly. In addition, most
DOS software expects text mode to be 80 characters wide and if the Horizontal Offset is modified
(in the CRTC) , the display will get a “barber pole” effect, instead of being clipped.
Programming and Driver Considerations
Most OEMs using the SPC8106 on smaller than VGA standard panels will be doing so for custom
applications. To aid in the development of these custom applications, we recommend the follow-
ing:
The mode set will act like Mode 12h (planar graphics) in memory planes, colors and memory
addresses and will make it very easy for OEMs to develop software in Mode 12h on a standard
VGA to port to this new environment. For graphics mode applications, remember to modify the
offset on your standard Mode 12h simulated environment to be the same as on the custom envi-
ronment you have just set, then when you are ready to move it to your new platform, change the
mode set from Mode 12h to a VESA Mode 4xh function call.
SPC8106
•
•
411-1.0
Set the appropriate mode number for your panel height as specified above.
Set the CRTC Offset register 3D4h index 13h to your appropriate width.
S-MOS Systems, Inc. • Tel: [phone] • Fax: [phone] • http://www.smos.com
X12-SP-002-03.1
BIOS Functional Specification
SP2-41