Digital Video Signal According to ITU-BT.R.601 (CCIR 601) - Digital Video and Audio Broadcasting Technology - page 84

direction. The most significant bit of the fourth code word is always 1. The
next bit (bit 8 in a 10 bit transmission or bit 6 in an 8 bit transmission)
flags the field; if this bit is set to zero, it is a line of the first field and if it is
set to one, it is a line of the second field. The next bit (bit 7 in a 10 bit
transmission or bit 5 in an 8 bit transmission) flags the active video area in
the vertical direction. If this bit is set to zero, then this is the visible active
video area and if not, it is the vertical blanking interval. Bit 6 (10 bit) or bit
4 (8 bit) provides information about whether the present code word is an
SAV or an EAV. It is SAV if this bit is set to zero and EAV if it is not.
Bits 5...2 (10 bit) or 3...0 (8 bit) are used for error protection of the SAV
and EAV code words. Code word 4 of the timing reference sequence
(TRS) contains the following information:

• F = Field (0 = 1st field, 1 = 2nd field)
• V = Vertical blanking (1 = vertical blanking interval active)
• H = SAV/EAV identification (0 = SAV, 1 = EAV)
• P0, P1, P2, P3 = Protection bits (Hamming code)

Neither the luminance signal (Y) nor the color difference signals (C B ,
C R ) use the full dynamic range available for them. There is a prohibited
range which is reserved as headroom, on the one hand, and, on the other
hand, allows SAV and EAV to be easily identified. A Y signal ranges be-
tween 16 and 64 decimal (8 bits) or 240 and 960 decimal (10 bits).

255/1023 255/1023

700 mV 235/940 350 mV 240/960

Y C

B /C R

0 mV 128/512

0 mV 16/64 350 mV 16/64

0

0

Fig. 4.4. Level diagram