SPC8106 S-MOS Systems, SPC8106 Datasheet - Page 128

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

For monochrome LCD modes, the VGA palette has been replaced by an internal 256x6 bit Gray
Scale Lookup Table. This lookup table operates in a similar manner as the VGA palette it
replaces, with its registers at the same I/O addresses.
For mode 256 color modes, the LCD controller will display a maximum of 64 shades of grey on a
monochrome LCD rather than the 256 of 256k colors on a CRT monitor. These 64 shades of gray
are achieved by using 16 gray-level frame-rate modulation plus dithering. For modes other than
256 color modes, the controller will display up to 16 shades of gray using frame-rate modulation.
Because of the smaller number of grey shades displayable on the LCD, a method of mapping col-
ors originally intended for display on a 16/256 color CRT monitor onto a 16/64 gray LCD panel is
required. Hardware is provided to map the RGB (18 bit) values that are written to the lookup table
by software expecting to program a regular VGA palette. These RGB values are mapped using 1
of 2 selectable schemes into 6 bit gray scale values that are stored in the lookup table.
For color LCD modes, the VGA palette is replaced by an internal 256 x 12 bit color lookup table.
This lookup table operates identically to the VGA palette it replaces except only the most signifi-
cant 4 bits of each of the 6 bit VGA R, G, B color values are stored. This allows a maximum of 256
colors displayed (in 256 color modes) on a color LCD out of a palette of 4096 possible colors.
For CRT display, the external RAMDAC supports the full 256 of 256k colors. If CRT mode is
enabled and AUX[0B] bit 6 = 0, writes to the RAMDAC registers will also go to the internal LUT
registers. An Auxiliary Register bit allows reading from either the external RAMDAC or internal
LUT registers in this case.
Details
This section gives a list of register bits in the SPC8106 that are different to the VGA standard.
Only differences are listed here. Any bits not mentioned are the same as the IBM VGA. For a
complete list of the actual SPC8106 registers see “I/O Register Summary” on page 89.
Misc. Output Reg. (3C2h W, 3CCh R)
bit 3
bit 1
Input Status Reg. 0 (3C2h R)
bit 4
Input Status Reg.1 (3DAh R)
bits 5-4
bits 2-1
Feature Control Reg. (3DAh W, 3CAh R)
Hardware Functional Specification
SP1-86
Lookup Table for LCD Display
S-MOS Systems, Inc. • Tel: [phone] • Fax: [phone] • http://www.smos.com
Clock Select bit 1
Read/write only. No other effect in hardware.
Enable DRAM
Read/write only. No other effect in hardware.
Switch Sense bit
Deleted.
Diagnostic
Deleted.
Light Pen
Read Only as 0,1.
Register not supported.
X12-SP-001-07
411-1.0
SPC8106