CS4954 datasheet(17/56 Pages) CIRRUS

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CS4954 CS4955

DS278PP4

VSYNC stays low for 2.5 line-times and transitions

high with the beginning of line 315. Video input on

the V [7:0] pins is expected between line 336

through line 622.

5.2.7. Progressive Scan

The CS4954/5 supports a progessive scan mode in

which the video output is non-interlaced. This is

accomplished by displaying only the odd video

field for NTSC or PAL. To preserve precise

MPEG-2 frame rates of 30 and 25 per second, the

CS4954/5 displays the same odd field repetitively

but alternately varies the field times. This mode is

in contrast to other digital video encoders, which

commonly support progressive scan by repetitively

displaying a 262 line field (524/525 lines for

NTSC). The common method is flawed: over time,

the output display rate will overrun a system-clock-

locked MPEG-2 decompressor and display a field

twice every 8.75 seconds.

5.2.8. NTSC Progressive Scan

VSYNC will transition low at line four to begin

field one and will remain low for three lines or

2574 pixel cycles (858 × 3). NTSC interlaced tim-

ing is illustrated in Figure 9. In this mode, the

CS4954/5 expects digital video input at the V [7:0]

NTSC Vertical Timing (odd field)

Line

HSYNC

VSYNC

FIELD

NTSC Vertical Timing (even field)

PAL Vertical Timing (odd field)

PAL Vertical Timing (even field)

264

265

266

267

268

269

270

271

265

311

312

313

314

315

316

317

318

Line

HSYNC

VSYNC

FIELD

Line

HSYNC

VSYNC

FIELD

Line

HSYNC

VSYNC

FIELD

Figure 6. Vertical Timing

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