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ADV7181C Teletext decoding

Question asked by XavE Employee on May 11, 2010
Latest reply on May 11, 2010 by XavE

We are providing a PAL signal with Teletext system B (WST) to the ADV7181C.


We use the recommended ADI script for CVBS and set register 0x62 in the user sub map to value 0xB5. This enables the insertion of VBI decoded data into the ancillary 656 stream, and sets the ancillary data output mode to Byte Mode.


We fix the teletext data from our source to some predetermined values (0xFE and 0x7F) repeating. When we read back the ancillary data from the digital output of the ADV7181C, we see that the data in the VBI words are shifted by 5 bits left (to the MSB).


We are also reading back the wrong framing code. We read 0xEA instead of 0x27 (in the reversed order of transmission).


How can this be fixed?