BT856 datasheet(20/54 Pages) ETC

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CIRCUIT DESCRIPTION

Video Timing

Bt856/7

Subcarrier Phasing

In order to maintain correct SC-H phasings, subcarrier phase is set to zero on the

falling edge of HSYNC* associated with VSYNC* every four (NTSC) or eight

(PAL) ﬁelds, unless bit D3 of register 0xDE is set to a logical one.

In slave mode, falling HSYNC* may lag falling VSYNC* by 1/4 scan line but

cannot precede falling VSYNC* by more than 14 CLOCK periods for correct

SC-H reset.

Setting D3 to one may be useful in situations where the ratio of

CLOCKS/HSYNC* edges in a color frame is non-integer, which could produce a

signiﬁcant phase impulse by resetting to zero.

For a perfect clock input, the burst frequency is 4.43361875 MHz for PAL–B,

D, G, H, I, N, 3.57561149 for PAL–M, 3.58205625 for PAL–N (Argentina),

3.579545 MHz for NTSC interlaced, and 3.579515 MHz for NTSC noninterlaced.

Vertical Blanking

Intervals

For interlaced NTSC/PAL–M, scan lines 1–9 and 263–272, inclusive, are always

blanked regardless of the BLANK* input. There is no setup on scan lines 10–21

and 273–284, inclusive, allowing the generation of video test signals, timecode,

and other information by controlling the pixel inputs appropriately (except for

lines controlled by closed caption or Macrovision generation).

For interlaced PAL–B, D, G, H, I, N, N-Argentina, scan lines 1–6, 311–318, and

624–625, inclusive, during ﬁelds 1, 2, 5, and 6, are always blanked regardless of

the BLANK* input. During ﬁelds 3, 4, 7, and 8, scan lines 1–5, 311–319, and

624–625, inclusive, are always blanked regardless of the BLANK* input. The re-

maining scan lines during the vertical blanking interval may be used for the gen-

eration of video test signals, timecode, and other information by controlling the

pixel inputs appropriately.

Alternately, all displayed lines in the vertical blanking interval (10–21 and

273–284 for interlaced NTSC/PAL–M; 7–13 and 320–335 for interlaced PAL–B,

D, G, H, I, N, N-Argentina) may be forced blanked by setting bit D2 to a logical

one in register 0xDE (except for caption lines controlled by bit D6 and D7 or Mac-

rovision process).

For noninterlaced NTSC/PAL–M, scan lines 1–9, inclusive, are always blanked

regardless of the BLANK* input. For noninterlaced PAL–B, D, G, H, I, N, N-Ar-

gentina, scan lines 1–6 and 311–312, inclusive, are always blanked regardless of

the BLANK* input.

Bit D2 at register 0xDE will blank lines 10–21 for NTSC/PAL–M or lines 7–23

for PAL–B, D, G, H, I, N, N-Argentina, except for closed captions on lines 21 (22)

and 284 (335), controlled by bits D6 and D7, or for Macrovision process.

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