saa6712e NXP Semiconductors, saa6712e Datasheet - Page 49

• Manufacturer Part Number: saa6712e
• Description: Xga Rgb To Tft Graphics Engine
• Manufacturer: NXP Semiconductors

Philips Semiconductors
8.8.2
The start of the horizontal sync pulse is defined in
ovl_hs_start and the polarity in ovl_hs_pol. The sync pulse
length is defined in ovl_hs_length (see Fig.14). It is
possible to generate a Hsync pulse from one clock cycle
length up to longer than the horizontal overlay data.
The vertical sync pulse starts at ovl_vs_start and is always
one output frame line long.
8.8.4
All of the above mentioned functions will only work during
internal processing of valid video data, and not during
internal blanking regions. This can give problems if the
overlay window is displayed at the left border of the picture
because the first pixels of a line will be processed due to
the internal pipeline structure. To overcome this, the
OVCLK can be gated to disable data processing by the
external OSD controller during internal blanking. Clock
gating is enabled by clk_gating_on.
8.9
The colour correction unit can be used to perform gamma
correction, change of brightness, and so on. This can be
achieved by means of a look-up table. Each colour
component value in an RGB pixel is used as a pointer into
this table. The value from the table will replace the
incoming colour.
1999 Aug 25
handbook, full pagewidth
XGA RGB to TFT graphics engine
Colour correction
S
OVCLK
OVACT
YNC GENERATION
OVCLK
OVHS
OVA
OVB
GATING
Fig.14 Hsync generation and data sampling (Hsync latency = 2).
ovl_hs_start
ovl_hs_latency
ovl_hs_length
O0
O1
49
8.8.3
Data sampling from the two ports OVA and OVB starts
from the beginning of the horizontal sync pulse, but the
number of clocks defined in ovl_hs_latency will decide
when reading data from the overlay port will start
(see Fig.14). The end of the sync pulse is not important.
Various tables exist for R, G, and B components.
Programming of a table must be performed using the
programming registers 47 to 49 (see the colour correction
section of the programming register Table 5). It must be
decided which component table should be written to
(red_prog, green_prog, blue_prog). In colour_index the
start address or the first incoming colour value for
programming must be written. Then subsequent writing to
colour_value fill the table. At this address the I
address auto-increment stops, but the value programmed
into colour_index will be incremented. It is possible to write
to more than one table by enabling of programming
multiple colour components.
If the colour correction unit is switched to bypass mode
(when colour_correction_on is not asserted), the incoming
colours are used for further processing.
Writing to the colour correction table is possible during
data processing.
O2
O3
ovl_h_length
D
O4
O5
ATA SAMPLING
O6
O7
O8
O9
Preliminary specification
SAA6712E
MHB259
2
C-bus