BT856 datasheet(18/54 Pages) ETC

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Brooktree®

CIRCUIT DESCRIPTION

Video Timing

Bt856/7

sumed. The frequency of operation (square pixels or CCIR) for both PAL and

NTSC is detected by counting the number of clocks per line. The sampling note is

assumed to be 13.5 MHz unless the exact horizontal count for square pixels,

±1

count, is detected in between two successive falling edges of HSYNC*.

NOTE:

Square pixel 625-line operation with this sequence requires one frame to

stabilize.

FIELD Output

The FIELD output indicates whether an odd ﬁeld (logical zero) or even ﬁeld (log-

ical one) is being generated. Field changes are detected by the falling edge of

VSYNC*. FIELD is output following the rising edge of CLOCK. Unless special

HSYNC* timing is programmed, FIELD output transitions low, two CLOCK pe-

riods following the falling edge of HSYNC* at the beginning of an odd ﬁeld.

This corresponds directly to the bottom/top* convention of some MPEG

decoders.

Pixel Blanking

BLANK* is registered on the rising edge of CLOCK. For RGBOUT mode, RGB

video is blanked for each clock period in which the BLANK* input is low. For vid-

eo outputs, BLANK* is pipelined to match the luminance and chrominance paths

and is applied to the digital video before analog conversion. The automatic hori-

zontal blanking sequence described in Table 10 (in the PC Board Considerations

section) take precedence over the BLANK* input.

Burst Blanking

For interlaced NTSC/PAL–M, color burst information is automatically disabled on

scan lines 1–6 and 264–269, inclusive. (SMPTE line numbering convention.)

For interlaced PAL–B, D, G, H, I, N, N-Argentina, color burst information is

automatically disabled on scan lines 1–6, 310–318, and 623–625, inclusive, for

ﬁelds 1, 2, 5, and 6. During ﬁelds 3, 4, 7, and 8, color burst information is disabled

on scan lines 1–5, 311–319, and 622–625, inclusive.

For noninterlaced NTSC/PAL–M, color burst information is automatically dis-

abled on scan lines 1–6 and 261–262, inclusive.

For noninterlaced PAL–B, D, G, H, I, N, N-Argentina, color burst information

is automatically disabled on scan lines 1–6 and 310–312, inclusive.

See Figures 3–6.

Digital Processing

Once the input data is converted into internal YUV format, the UV components are

low-pass ﬁltered with a ﬁlter response shown in Figure 7 (linearly scalable by

clock frequency). The Y and ﬁltered UV components are upsampled to CLKX2

frequency by a digital ﬁlter whose response is shown in Figure 8.

Chrominance Disable

The chrominance subcarrier may be turned off by setting bit D5 of register subad-

dress 0xDE to a logical one. This kills burst as well, providing luminance only sig-

nals on the CVBS outputs and a static blank level on the C/R output

(RGBOUT=0).

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