SAA8115HL データシートの表示（PDF） - Philips Electronics

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SAA8115HL

Digital camera USB interface

Philips Electronics 

Philips Semiconductors

Digital camera USB interface

Preliminary specification

SAA8115HL

8 FUNCTIONAL DESCRIPTION

8.1 Video synchronization

The video synchronization module is capable of locking to

the video signal implementing a horizontal gate signal

HREF (HREF = HIGH when data is valid) and a VS signal

indicating the start of a new video frame.

8.2 Frame rate converter and SDRAM interface

An optional SDRAM (external) can be accessed using the

SDRAM interface which is integrated in the SAA8115HL.

Pinning and functionality is based on the NEC

µPD4516161 (16 Mbits) and the NEC µPD4564163

(64 Mbits).

When used, the memory is placed at the video input of the

SAA8115HL before prefilter, scaler and compression

engine. At this point only YUV 4 : 2 : 2 formatted data is

available.

The use of the SDRAM is twofold:

• Lowering the frame rate. The memory enables to store

one frame of video accumulated at a specific rate and to

read it out at a lower frame rate. For interline VGA

sensors, the input frame rate is either 30 fps or 15 fps.

It can be lowered with a factor of 2, 3, 6, 16 or 32.

For CIF or medium resolution PAL, the input frame rate

is only 30 fps

• Enhanced snapshot mode. Storage of full size VGA

pictures in 4 : 2 : 2 format which can be retrieved upon

dedicated software command.

8.3 Video formatter: downsampler and cutter

This block is used to achieve the required output format

from the specified sensor formats (see Fig.3). It works for

YUV 4 : 2 : 2 only. In RAW mode this block is by-passed to

create a full resolution snapshot.

Horizontally a downsampling from 512 or 640 to either

384, 320, 192 or 160 or from 352 to 176 is necessary.

The horizontal downsampling is performed with the use of

a Variable Phase Delay filter (VPD-4). This filter can

realize the needed downsample factors. To avoid aliasing,

this module also contains a prefilter which has four modes:

• No filter for medium resolution PAL (512 × 288) to CIF

(352 × 288) or SIF (320 × 240)

• Prefilter A (3 taps) for VGA (640 × 480) to CIF or SIF,

CIF to QCIF (176 × 144) or QSIF (160 × 120)

• Prefilter B (7 taps) for medium resolution PAL to QCIF

or QSIF

• Prefilter A combined with prefilter B-comb (13 taps) for

VGA to QCIF or QSIF.

Prefilter B-comb is similar to prefilter B but inserts extra

taps with amplification 0.

The vertical downsampling in PAL mode is from CIF to

QCIF only. This is done via a vertical filter A (3 taps).

In VGA mode a 4 taps polyphase filter is applied to scale

from 640 × 480 to CIF and QCIF.

From a full size QCIF picture a sub-QCIF (128 × 96) cut

can be made. For the zoomed sub-QCIF format, the origin

(upper left corner) is programmable via SNERT in 13 steps

(both horizontally and vertically), so that an electronic pan

and tilt is possible.

The incoming 4 : 2 : 2 data is vertically filtered to 4 : 2 : 0,

in order to be sent over USB, by throwing away colour

samples. In the even lines the V-samples are discarded, in

the odd lines the U-samples.

2000 Jan 27

11

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