saa6703h NXP Semiconductors, saa6703h Datasheet - Page 75

• Manufacturer Part Number: saa6703h
• Description: Xga Dual Input Flat Panel Controller.
• Manufacturer: NXP Semiconductors

Philips Semiconductors
The text shadow is generated over the whole OSD and just
displayed in the enabled characters. So it is not character
bound. This means that a neighbouring ‘non-shadowed’
character can throw part of its shadow in the shadow
allowed character. Also the text shadow is only able to
work correct if the whole OSD is inside the picture
boundaries and will be turned off automatically if this is not
the case. The generated shadow is treated as
background, so the shadow is alpha-blended with the
background alpha-blending factor, but the shadow is
never displayed transparent.
During any configuration with the cursors in either the OSD
window or one of the pixel addresses be aware that the
cursor will ‘wrap around’ if the calculated address exceeds
the physical memory address space.
7.15
The colour look-up table unit (or gamma correction unit)
performs gamma correction and colour component
brightness and contrast adjustment. Each 8-bit RGB
component value is mapped to a programmable 10-bit
value by using it as an index for a look-up table that returns
the corresponding image value. The colour components
are processed by three independent tables.
The output value for each index value is programmed by
writing the 8-bit index to register CL_INDEX and then
programming registers CL_VALUE_HI (02H) and
CL_VALUE_LO (03H) with the 10-bit image value. Each of
the three look-up tables is individually activated for
programming by setting red_prog, geen_prog or
blue_prog respectively to logic 1.
The activated tables are updated with the new value pair
when the lower byte of CL_VALUE_LO (03H) was written.
To support quick programming of consecutive values, the
index value is incremented after every completed write, so
CL_INDEX does not have to be reprogrammed for every
data pair. Also the I
overridden when writing to CL_VALUE_LO. Instead the
subaddress for the next write is determined according to
register CL_CTRL. If quick_prog is set logic 0 the
subaddress for the next write is set back to 02H
(CL_VALUE_HI); otherwise it remains 03H
(CL_VALUE_LO), which allows sequential writes of the
lower byte only.
As the look-up tables can only be either written or read at
the same time, during write operations with activated
colour look-up the tables are bypassed. To avoid any
influence on the output picture, write_hsynced can be set
to logic 1 to update the look-up tables only during
2004 Apr 01
XGA dual input flat panel controller
Colour look-up table
2
C-bus subaddress auto-increment is
75
horizontal blanking, which slows down programming
speed.
Colour look-up is enabled by setting cc_on to logic 1;
otherwise the colour look-up tables are in bypass mode
and the image values consist of the original value in the
upper eight bits and both LSBs are set to logic 0.
Programming of the look-up tables is possible in bypass
mode or during data processing.
7.16
The dither unit improves the visual quality of displays with
only 6-bit or 8-bit physical colour resolution to a virtual
colour depth of 10 bits. This is achieved through temporal
variation of the physically possible colour values.
To reduce artefacts of the temporal variation neighbouring
pixels follow different sequences of variation. The dithering
unit registers are mapped to page 10, registers
80H to 83H.
Dithering is switched on if dither_bypass is set to logic 0;
otherwise the dithering unit is bypassed. The colour depth
of the target display is selected by dither_out_bits. For an
8-bit panel dither_out_bits is set to logic 1; for a 6-bit panel
the programming bit is set to logic 0.
Bits dither_idx_ofs_reg[2:0] give a choice of variation
sequences (see Table 50). Best quality is expected for
most displays with the setting random.
Table 50 Dithering sequences; note 1
Note
1. X = don’t care.
Additionally, the unit adds LSB noise to the 10-bit colour
values from the colour look-up table, when enabled by
dither_add_noise = 1, which improves visual display
quality of certain 10-bit displays (e.g. plasma displays).
The noise includes only one LSB if dither_noise_mag is
set to logic 0; otherwise two LSBs.
Configuration parameters dither_colmap,
dither_rand_mono and dither_rand_mode are for test
purposes and should be left in their reset values.
dither_idx_ofs_reg[2:0]
Dithering unit
1XX
000
001
010
011
constant zero
2
4
5
random
2 Bayer
4 Bayer
5 special
Product specification
SEQUENCE
SAA6703H