SAA6721E Datasheet, PDF (55/72 Pages) NXP Semiconductors – SXGA RGB to TFT graphics engine

Philips Semiconductors
SXGA RGB to TFT graphics engine
Preliminary specification
SAA6721E
8.8.2 SYNC GENERATION
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.19). 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.
8.8.3 DATA SAMPLING
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.19). The end of the sync pulse is not important.
handbook, full pagewidth
OVCLK
OVHS
OVA
OVB
OVACT
ovl_hs_start
ovl_hs_length
ovl_hs_latency
ovl_h_length
O0
O2
O4
O6
O8
O1
O3
O5
O7
O9
Fig.19 Hsync generation and data sampling (Hsync latency = 2).
MHB259
8.8.4 OVCLK GATING
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 Colour space matrix
The back-end processing of the SAA6721E and the TFT
panels require RGB video data. So the built-in colour
space matrix is used to convert video data from YUV
space into RGB space. It can be enabled by setting
csm_bypass to logic 0 (see general configuration section
of the programming register Table 7), otherwise the colour
space converter will be bypassed.
8.10 Colour correction
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.
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 7). 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 I²C-bus
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.
1999 May 11
55