SAA7201 データシートの表示（PDF） - Philips Electronics

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SAA7201

3.3 V, integrated MPEG2 AVG decoder / QFP160 Package

Philips Electronics 

Philips Semiconductors

Integrated MPEG2 AVG decoder

Objective specification

SAA7201

CURSOR PROCESSING

Additionally to the above defined graphics boxes one

cursor can be activated on the screen. Since the cursor

data is fully stored locally, no overlapping restriction apply

to this box so the cursor can moved over the entire screen.

The cursor can be as large as 1 kpixel with a 2 bits/pixel

colour depth. Obviously data transfer can be done on DMA

basis and need only be performed when a cursor is

required or when its contents must be modified.

The cursor XY dimensions (where the Y dimension refers

to frame lines) can be selected between 8 × 128, 16 × 64,

32 × 32, 64 × 16 and 128 × 8. On top of these shapes, a

zoom with a factor 2 can be applied in both directions

independently.

The cursor pixels will be translated via a 4-entry CLUT to

YUV colours and a transparency factor T. The resolution

of the YUV parameters is 6, 4, 4 bits respectively.

The T parameter is coded in 2 bits to enable the mixing

with video and graphics in 4 steps being 100% (cursor

only), 50%, 25% and 0% (fully transparent cursor).

Display unit

Before feeding the MPEG decoded and graphical data to

the output, a display unit re-formats the MPEG specific

4 : 2 : 0 format to CCIR-601 4 : 2 : 2 format and performs

a mixing between video and graphics where required.

The output picture can be up to 720 × 576 pixels at 50 Hz

or 720 × 480 pixels at 60 Hz.

A schematic representation of this unit is shown in Fig.11.

• In a first step a selected window can be retrieved from

the decoded MPEG data. This might be useful for e.g.

pan and scan operations for aspect ratio conversion.

• In case the resulting number of pixels per line does not

match the 720 pixels/line output format a horizontal

scaler can be activated. This scaling unit can transform

any number of bits below 720 to the required output

format. Internally a poly-phase filter is used which

performs a 64 phases interpolation. Not only

up-conversion but also down-conversion is supported

up to a scaling by a factor 2. Thus horizontal scaling can

be performed in a range from 0.5 up to 64. In practice

the maximum up-conversion factor will be less or equal

to 4.

• In vertical direction the picture can be expanded or

scaled down, in both cases by a factor 2. Expansion with

a factor 2 might be relevant for the up-conversion of SIF

resolution pictures to full screen. The factor 2 scaling, if

combined with the appropriate horizontal scaling, results

is 1⁄4 picture thus freeing-up a large screen area for

graphics. This might be very useful for electronic

program guide applications. It should be noted that in

case of picture compression an anti-aliasing filter can be

activated.

• Shifting: when the resulting MPEG picture is smaller

than the 720 × 576 (480) display format, this picture can

be located anywhere on the display screen.

Moreover, the non-covered area can be given any

background colour.

• Clipping: the amplitude of the MPEG decoded and

re-scaled video signal is kept within the range 16 to 235

for luminance and 16 to 240 for both chrominance

components.

handbook, full pagewidth

MPEG

decoded

picture

WINDOW

EXTRACTION

SCALING

SHIFTING

CLIPPING

CHROMA

UP-CONVERSION

64 STEP

MIXER

4 STEP

MIXER

OUTPUT

FORMAT

to digital

CVBS

encoder

1997 Jan 29

GRAPHICS

CURSOR

MGD331

Fig.11 Display unit.

18

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