CS4954 datasheet(18/60 Pages) CIRRUS

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CS4954 CS4955

DS278F6

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 pseudo-progessive scan

mode for which “odd” and “even” numbered line

information is presented in “odd” numbered line

positions by varying the vertical blanking timing.

This preserves precise MPEG-2 frame rates of 30

and 25 frames per second. 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]

pins for 240 lines beginning on active video line 22

and continuing through line 261.

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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