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Trying to extract teletext data using Ancillary Data

Category: Hardware
Product Number: ADV7180

I'm trying to extract teletext data using Ancillary Data on ADV7180.

I have a video input from TV Pattern Generator with teletext B.

Video part is working well.

But when I try to get Ancillary Data I got framing code 0xEA but not 0x27 or 0xE4.

I have confirmed that from TV generator framing code is 0xE4.

When I switch to  VPS, WSS, data framing code is match.

Why only teletext framing code not 0x27?

Registers I have set for teletext.

reg 0x03 = 0x8C; // VBI_EN

reg 0x0e = 0x20; // access registers. Table 103.

reg 0x62 = 0xB5; // ADF_ENABLE, Byte type

Please advise.

  • Hi,

    For ancillary data : The SDP can handle a variety of vertical blanking interval (VBI) data services, such as closed captioning (CCAP), wide screen signaling (WSS),copy generation management system (CGMS) and teletext data slicing for world standard teletext (WST). Data is transmitted via the 8-bit video output port as ancillary data packets (ANC).

    There is a bit that is set to "1" by default which affects the framing code in ancillary output.

    This is bit 4 of Register 0x61 in the user sub map. It is called AUTO_DETECT_GS_TYPE, and it enables the auto identification of Gemstar type.Setting this bit to "0" will fix the teletext decoding issue observed. The framing code will then be 0x27 (in the reversed order of transmission) as expected. There will not be any shift in the VBI words.

    Thanks,
    Varshini K.

  •  Hi VarshiniK,

    Thank you for your advise. I can confirm that disabling this bit gets right framing code. But there is another question.

    Teletext using Data line from 12 to 15 and 21 in the odd fields.

    And from 322 to 328 and 334 in the even fields.

     

    Gemstar using

    23 Gemstar_1×  24 Gemstar_1× 25 Gemstar_1×

    286 Gemstar_1× 287 Gemstar_1× 288 Gemstar_1× and only in NTSC.

     

    I am using PAL and why VDP detects it as Gemstar ?

    Does it mean that I have to change bit 4 of Register 0x61 when NTSC and PAL ?

    Please advise.

  • Hi,

    Does it mean that I have to change bit 4 of Register 0x61 when NTSC and PAL ?

      Please change 0x61[4] and check it for PAL input.

      Kindly note that, In short, while Gemstar's VCR Plus+ system operates in both NTSC and PAL regions, the VDP needs to be designed for the specific video standard (NTSC or PAL) to properly process the data embedded in the VBI. This affects how the system interacts with the hardware (like VCRs and TVs).

      Also refer (+) ADV7181C Teletext  errors - Q&A - Video - EngineerZone

    Thanks,

    Poornima