SAA7131E Datasheet, PDF (29/66 Pages) NXP Semiconductors – Global standard low-IF demodulator and PCI audio and video decoder for analog TV

NXP Semiconductors
SAA7131E
Global standard low-IF and PCI audio and video decoder
7.6.7 VBI data
The Vertical Blanking Interval (VBI) is often utilized to transport data over analog video
broadcast. Such data can closely relate to the actual video stream, or just be general data
(e.g. news). Some examples for VBI data types are given below:
• Closed Caption (CC) for the hearing impaired (CC, on line 21 of first field)
• Intercast data [in USA coded in North American Broadcast Text System (NABTS)
format, in Europe in World System Teletext (WST)], to transmit internet related
services, optionally associated with actual video program content
• Teletext, transporting news services and broadcast related information, Electronic
Program Guide (EPG), widely used in Europe (coded in WST format)
• EPG, broadcaster specific program and schedule information, sometimes with
proprietary coding scheme (pay service), usually carried on NABTS, WST, Video
Programming System (VPS), or proprietary data coding format
• Vertical Interval Time Codes (VITC) as inserted in camcorders e.g. use for video
editing
• Copy Guard Management System (CGMS) codes, to indicate copy protected video
material, sometimes combined with format information [Wide Screen Signalling
(WSS)].
This information is coded in the unused lines of the vertical blanking interval, between the
vertical sync pulse and the active visible video picture. So-called full-field data
transmission is also possible, utilizing all video lines for data coding.
The SAA7131E supports the capture of VBI data, by the definition of a VBI region, which
is captured as raw VBI samples. These samples are sliced and decoded by software on
the host CPU. The raw sample stream is taken directly from the ADC and is not processed
or filtered by the video decoder. The sampling rate of raw VBI data can be adjusted to the
needs of the data slicing software.
7.6.8 Signal levels and color space
Analog TV video signals are decoded into their various components, luminance and color
difference signals (YUV) or its digital form Y-C_B-C_R. ITU-R BT.601 defines 720 pixel/line
(corresponding to a sampling rate of 27 MHz divided by two), and a certain relationship
from level to number range; see Figure 9.
The video components do not use the entire number range, but leave some margin for
overshoots and intermediate values during processing. For the raw VBI samples there is
no official specification how to code, but it is common practice to reserve the lower quarter
of the number range for the sync, and to leave some room for overmodulation beyond the
nominal white amplitude; see Figure 10.
The automatic clamp and gain control at the video input, together with the automatic
chroma gain control of the SAA7131E, ensures that the video component stream at the
output complies to the standard levels. Additional brightness, contrast, saturation and hue
control can also be applied to satisfy special needs of a given application. The raw VBI
samples can be adjusted independent of the active video.
SAA7131E_3
Product data sheet
Rev. 03 — 19 May 2008
© NXP B.V. 2008. All rights reserved.
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