BIT SERIAL DIGITAL INTERFACE DEFINED BY SMPTE 292M.

HDTV digital component video is produced by applying a 4:2:2 sampling structure to the analog signal. The luminance component (Y) is sampled at 74.25 MHz, the colour difference components U & V) are both sampled at 37.125 MHz.

The Y stream is quantised to 10 bits resolution and Timing Reference Signals (TRS) are added at the beginning and end of the horizontal video blanking period.

The U & V streams are also quantised to 10 bits and then interleaved to give a C stream at 74.25 MHz. TRS are added at the beginning and end of the horizontal video blanking period.

The 74.25MHz Y and C streams are then interleaved to produce a single stream at 148.5MHz.

The TRS at the end of the horizontal blanking period is called Start of Active Video (SAV) it consists of 4 words:

1) 3FF hex ie all '1;s

2) 000 hex ie all '0's

3) 000 hex ie all '0's

4) XYZ, which determines the type of TRS pulse, consisting of:

Bit 9: Always '1'

Bit 8: 0=frame 1, 1=frame 2

Bit 7: 0=normal 1=field blanking

Bit 6: 0=SAV 1=EAV

Bit 5: Bits used for Hamming correction.

Bit 4: Bits used for Hamming correction.

Bit 3: Bits used for Hamming correction.

Bit 2: Bits used for Hamming correction.

Bit 1: Always 0

Bit 0: Always 0

The TRS at the beginning of the horizontal blanking period is called End of Active Video (EAV) it consists of 8 words: The first 4 are the same as for SAV, followed by 2 words containing the current line number and 2 words containing a Cyclic Redundancy Check (CRC) for all the preceding words in the line.

The period between EAV and SAV is not used by normal video and may be used for embedded audio or timecode data.

ILLEGAL VALUES

The values 000 and 3FF hex are used solely by TRS pulses (EAV & SAV) they must not appear anywhere in the active video area.

OUT OF GAMUT

Values apart from the illegal values which should not be used.

Luminance is defined as being between peak white, 700mV (3AC hex) and black 0 mV (040 hex) Chroma is defined as being between max positive 350mV (3C0 hex) and max negative - 350mV (040 hex). Values above or below these values are termed 'Out of Gamut'.

The data is scrambled and then serialised using a None Return to Zero (NRZ) code to produce a 1.485 GHz signal.

PARALLEL DIGITAL INTERFACES

Several parallel video Standards can be used with the above serial interface. These are defined in SMPTE 274M for 1920 x 1080 scanning and SMPTE 296M for 1280 x 720 scanning.

SMPTE 274M

Several sub-standards for this are defined:

1920 x 1080/60/2:1

1920 samples/active line 1080 active line/frame 30 Hz Interlaced scan.

74.25 MHz Sample frequency 2200 total samples/line 1125 total lines/frame

1920 x 1080/59.94/2:1

1920 samples/active line 1080 active line/frame 29.97 Hz Interlaced scan.

74.176 MHz Sample frequency 2200 total samples/line 1125 total lines/frame

This standard gives an exact frame rate compatibility with NTSC.

1920 x 1080/50/2:1

1920 samples/active line 1080 active line/frame 25 Hz Interlaced scan.

74.25 MHz Sample frequency 2640 total samples/line 1125 total lines/frame

1920 x 1080/30/1:1

1920 samples/active line 1080 active line/frame 30 Hz Progressive scan.

74.25 MHz Sample frequency 2200 total samples/line 1125 total lines/frame

1920 x 1080/29.97/1:1

1920 samples/active line 1080 active line/frame 29.97 Hz Progressive scan.

74.176 MHz Sample frequency 2200 total samples/line 1125 total lines/frame

This standard gives an exact frame rate compatibility with NTSC.

1920 x 1080/25/1:1

1920 samples/active line 1080 active line/frame 25 Hz Progressive scan.

74.25 MHz Sample frequency 2640 total samples/line 1125 total lines/frame

1920 x 1080/24/1:1

1920 samples/active line 1080 active line/frame 24 Hz Progressive scan.

74.25 MHz Sample frequency 2750 total samples/line 1125 total lines/frame

1920 x 1080/23.98/1:1

1920 samples/active line 1080 active line/frame 23.98 Hz Progressive scan.

74.176 MHz Sample frequency 2750 total samples/line 1125 total lines/frame

SMPTE 296M

Several substandards for this are defined:

1280 x 720/60/1:1

1280 samples/active line 720 active line/frame 60 Hz Progressive scan.

74.25 MHz Sample frequency 1650 total samples/line 750 total lines/frame

1280 x 720/59.94/1:1

1280 samples/active line 720 active line/frame 59.94 Hz Progressive scan.

74.176 MHz Sample frequency 1650 total samples/line 750 total lines/frame

EMBEDDED AUDIO

The period between EAV and SAV can be used to send embedded digital audio signals. This

is defined in SMPTE 299M. Up to 16 separate audio signals may be sent in a single video

channel. These are organised as four GROUPS of four signals, the four signals are often two

stereo pairs. Typically only one group will be used, giving two stereo pairs of audio. The

audio data is quantised in the sending equipment to 24 bits of resolution, usually at 48 KHz

sample rate in AES/EBU format. The digitised data is arranged in packets which are placed in

the EAV-SAV space.

The Header: (000, 3FF, 3FF)

Data ID: This contains the Audio group number.

Data block number: AES frames have 192 samples of audio data

Data Count: This contains the number of words that follow, always 218 hex

Clock: 2 words containing the number of video clocks that have elapsed between the first

word of EAV and the time the audio sample was made, it is used by the receiving equipment

to reconstruct the audio signal with the correct phase delay.

Audio Sample 1: Consists of four words

Audio Sample 2: Consists of four words

Audio Sample 3: Consists of four words

Audio Sample 4: Consists of four words

Error Correction Codes

Consist of six words used by the receiving equipment to detect or correct errors in the 24

words from the header to the last word of audio sample 4 inclusive.

Check Sum This is the sum of all previous words in the packet except the header words.

Each audio packet contains a sample of all four audio signals

eg: Channel 1 left, Channel 1 right, Channel 2 left and Channel 2 right.

Each audio signal requires 3 words to hold all 24 bits, thus each audio packet has 12 words of

audio data.

Typically one or two packets are sent in each EAV-SAV period.

These audio data packets are placed in the Chroma data stream only.

Audio Control Packets.

The audio control packet structure is similar to the audio data packet.

Data in the packet includes the audio sample rate eg 48 KHz,

the number of active channels out of the possible 4,

the delay information between Channel 1 audio and Channel 2

and delay information between Channel 3 audio and Channel 4.

Audio control packets are placed in the Luminance Stream, this is sent once per frame in the

second line after the switching point.

As with the video signal words consisting of all '1's or all '0's are not allowed.