cx25840 Conexant Systems, Inc., cx25840 Datasheet - Page 63

• Manufacturer Part Number: cx25840
• Description: Video Decoder And Broadcast Audio
• Manufacturer: Conexant Systems, Inc.

CX25840/1/2/3 Data Sheet
3.5.2
Figure 3-11. Vertical Scaling Block Diagram
102284B
8/3/05
VTG_HRESET_N
VTG_VRESET_N
LUMA_HSC[9:0]
CBCR_HSC9:0]
HSC_HACTIVE
VTG_VACTIVE
VS_INTRLACE
HSC_CBFLAG
VTG_AFD[3:2]
VSCALE[12:0]
CDP_DBLINE
VTG_FIELD
HSC_SKIP
VFILT[2:0]
VBLANK0
Vertical Scaling
The vertical scaling function is shown in
block is to scale down vertically by reducing the number of lines. In addition, special
functions are performed during SECAM mode for Dr/Db line-store and during PAL
mode for line averaging.
Dr/Db Line
Valid video data does not start until line 21 for NTSC and line 33 for PAL/SECAM. In
autoconfiguration mode, the default value for the vertical blanking delay, VBLANK
(0x474 an 0x475) is set to 22 and 34, respectively, for each video standard. This
register value, VBLANK, represents the number of half lines between the trailing
edge of a vertical reset (after the first nine lines, which contain equalization and
serration pulses) and the start of active video, while the VACTIVE (0x475 and 0x476)
registers represents the number of half lines in the vertical active region that enter the
vertical scaler.
As in the horizontal scaler, the two factors that determine the scaling process are the
number of active lines going into the vertical scaler and the number of desired lines
out of the scaler. The ratio of these two values determines the scaling ratio to be used
in the VSCALE formula below:
Vertical Scale Value (VSCALE) = (2
Thus, the vertical scaling ratio is determined by VACTIVE, the number of half lines
coming into the scaler and desired number of half lines output from the scaler. For
example, to achieve vertical scaling of an NTSC BT.656 full-resolution (487 active
half lines) image down to a half-resolution (244 active pixel) image, the scaling ratio
would simply be 2, Scaling Ratio = 487/244. Using this value in the vertical scaling
equation yields a value of VSCALE = 2
scale factor would be 4, Scaling Ratio = 487/122. Thus, the VSCALE register (0x41C
and 0x41D) value must be set to 2
Generator
Line Store
NOTE:
SECAM
Phase
Store
and
SECAM
VSKIP
PHASE[2:0]
PAL
CL_LUMA[9:0]
PL_LUMA9:0]
CL_CHROMA[9:0]
PL_CHROMA[9:0]
Only the 13 LSBs are used (& = logical AND).
Conexant
Coefficient
Coefficient
Generator
Generator
Chroma
Luma
16
CCLC[7:0]
CPLC[7:0]
YCLC[7:0]
YPLC[7:0]
– 3 x 2
16
– (Scaling Ratio–1) x 2
16
Figure
– 2
9
, 0x1A00.
9
(0x1E00). For 4:1 vertical scaling, the
Luma/Chroma
Interpolation
3-11. The primary purpose of this
Averaging
Filter and
PAL Line
Detailed Functional Description
9
) & 0x1FFF
LUMA_VSC[9:0]
CBCR_VSC[9:0]
VSC_VALID
VSC_FIELD
VSC_CBFLAG
VSC_HRESET
VSC_VRESET
VSC_HACTIVE
VSC_VACTIVE
102284_012
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