RIVA128ZX datasheet(52/85 Pages) STMICROELECTRONICS

52 / 85 page

128-BIT 3D MULTIMEDIA ACCELERATOR

RIVA128ZX

52/85

8.5

VBI HANDLING IN THE VIDEO PORT

RIVA128ZX supports two basic modes for VBI

data capture. VBI mode 1 is for use with the Philips

SAA7111A digitizer, VBI mode 2 is for use with the

Samsung KS0127 digitizer.

In VBI mode 1, the region to be captured as VBI

data is set up in the SAA7111A via the serial inter-

face, and in the RIVA128ZX under software con-

trol. The SAA7111A responds by suppressing

generation of SAV and EAV codes for the lines se-

lected, and sending raw sample data to the port.

The RIVA128ZX Video Port capture engine starts

capturing VBI data at an EAV code in the line last

active and continues to capture data without a

break until it detects the next SAV code. VBI cap-

ture is then complete for that field.

In VBI mode 2, the region to be captured as VBI

data is set up in a similar manner. The KS0127 re-

sponds by enabling VBI data collection only during

the lines specified and framed by normal ITU-R-

656 SAV/EAV codes. The RIVA128ZX Video Port

capture engine starts capturing data at an SAV

code controlled by the device driver, and contin-

ues capturing data under control of SAV/EAV

codes until a specific EAV code identified by the

device driver is sampled. VBI capture is then com-

plete for that field. The number of bytes collected

will vary depending on the setup of the KS0127.

8.6

SCALING IN THE VIDEO PORT

The RIVA128ZX Video Port allows any arbitrary

scale factor between 1 and 31. For best results the

scale factors of 1, 2, 3, 4, 6, 8, 12, 16, and 24 are

selected to avoid filtering losses. The Video Port

decimates in the y-direction, dropping lines every

few lines depending on the vertical scaling factor.

The intention is to support filtered downscaling in

the attached video decoder.

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