ANSI CTA-2020-2007 pdf download.Other VBI Waveforms
1 Scope
This standard, CEA-2020, specifies four Vertical Blanking Interval (VBI) waveforms in commercial use. The electrical properties of the waveforms are covered, but the meaning of the payload data is not. The waveforms apply to 525-line, interlaced (i.e. 480i) analog television signals. The waveforms may be present on analog inputs and analog outputs, but no conformance requirements about the actual presence of the waveforms are defined in CEA-2020. 2 References
2.1 Normative References
The following standards contain provisions that, through reference in this text, constitute normative provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards listed in Section 2.1.1.
6.1.3 System Considerations – Synchronization of TVG1x and Video
A set of bits associated with a given frame/field of video shall remain associated with that field but the respective frame could be delayed up to a maximum of 3 frame pipeline delay. Delaying the TVG1x data with respect to the active video information beyond this specification will result in errors.
6.2 TVG2x Waveform
This section describes the signal format used to encode data for transmission on NTSC video of the television picture in the VBI region. It contains important information related to both encoders and decoders. This information is provided to ensure compatibility between encoders and decoders.
6.2.1 Signal Locations
TVG2x shall be encoded with 51 bits per VBI line, corresponding to an approximate 1Mbps waveform. The 51 bits are defined by the clock run-in (8), Frame code (11), and 4 byte payload data (32).
6.2.2 TVG2x Waveform
The signal waveform shall be as defined in Figure 6. The Clock Run-In shall be a symmetrical sine wave with its maximum and minimum amplitudes being equal to the logic “1” and “0” levels respectively of the encoded data. The Clock Run-In shall also be in phase with all of the logic level transitions of the Start and Data bits. The 11 bit Frame Code bits shall follow the same specifications as the Data bits, but are always defined to be 10011101101 in binary. The signal specifications shall be as defined in Table 5, which also contains a section related to encoders and another section related to decoders. The specifications for these two sections are different to allow for distortions introduced by the transmission channel. The encoder shall be designed to produce an output as close to the nominal specifications as possible. The decoder should be designed to accept as large a variance from the nominal specifications as possible. The tolerances given for the decoder are suggested minimum tolerances.
IRE levels (i.e. Y) and timing information for Figure 6 are defined in Table 5. Other normative Figure 6 details follow:
a) All interval measurements shall be made from the midpoints (half amplitude) on all edges.
b) Regardless of where they are introduced in the signal, deviations due to source generated switching transients shall be no greater than ± 2 IRE. However, decoders should accept larger deviations that may be introduced by passing the signal through a transmission channel and/or signal security system.
c) If this signal format is used on both fields, the difference in the amplitudes of corresponding signal parameters between the two fields shall be no greater than ± 5 IRE as measured at the decoder input.
d) If only one of the two fields is being encoded, the other field shall not be altered.ANSI CTA-2020-2007 pdf download
