ADV7180WBSTZ datasheet(62/120 Pages) AD

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ADV7180

Data Sheet

Rev. G | Page 62 of 120

I2C READBACK REGISTERS

Teletext

Because teletext is a high data rate standard, the decoded bytes

are available only as ancillary data. However, a TTXT_AVL bit

has been provided in I2C so that the user can check whether the

VDP has detected teletext. Note that the TTXT_AVL bit is a

plain status bit and does not use the protocol identified in the

I2C Interface section.

TTXT_AVL, Teletext Detected Status, Address 0x78[7],

User Sub Map, Read Only

When TTXT_AVL is 0, teletext was not detected.

When TTXT_AVL is 1, teletext was detected.

WST Packet Decoding

For WST only, the VDP decodes the magazine and row address

of teletext packets and further decodes the packet’s 8 × 4

hamming coded words. This feature can be disabled using the

WST_PKT_DECODE_DISABLE bit (Bit 3, Register 0x60, user

sub map). This feature is valid for WST only.

WST_PKT_DECODE_DISABLE, Disable Hamming

Decoding of Bytes in WST, Address 0x60[3], User Sub Map

Setting WST_PKT_DECODE_DISABLE to 0 enables hamming

decoding of WST packets.

Setting WST_PKT_DECODE_DISABLE to 1 (default) disables

hamming decoding of WST packets.

For hamming-coded bytes, the dehammed nibbles are output

along with some error information from the hamming decoder

as follows:



Input hamming coded byte: {D3, P3, D2, P2, D1, P1, D0, P0}

(bits in decoded order)



Output dehammed byte: {E1, E0, 0, 0, D3', D2', D1', D0'}

(Di' – corrected bits, Ei error information).

Table 79. Error Bits in the Dehammed Output Byte

E[1:0]

Error Information

Output Data Bits

in Nibble

No errors detected

Okay

Error in P4

Okay

Double error

Bad

Single error found and corrected

Okay

Table 80 describes the WST packets that are decoded.

Table 80. WST Packet Description

Packet

Byte

Description

Header Packet (X/00)

1st

Magazine number—Dehammed Byte 4

2nd

Row number—Dehammed Byte 5

3rd

Page number—Dehammed Byte 6

4th

Page number—Dehammed Byte 7

5th to 10th

Control bytes—Dehammed Byte 8 to Byte 13

11th to 42nd

Raw data bytes

Text Packets (X/01 to X/25)

1st

Magazine number—Dehammed Byte 4

2nd

Row number—Dehammed Byte 5

3rd to 42nd

Raw data bytes

8/30 (Format 1) Packet

1st

Magazine number—Dehammed Byte 4

Design Code = 0000 or 0001

2nd

Row number—Dehammed Byte 5

UTC

3rd

Design code—Dehammed Byte 6

4th to 10th

Dehammed initial teletext page, Byte 7 to Byte 12

11th to 23rd

UTC bytes—Dehammed Byte 13 to Byte 25

24th to 42nd

Raw status bytes

8/30 (Format 2) Packet

1st

Magazine number—Dehammed Byte 4

Design Code = 0010 or 0011

2nd

Row number—Dehammed Byte 5

PDC

3rd

Design code—Dehammed Byte 6

4th to 10th

Dehammed initial teletext page, Byte 7 to Byte 12

11th to 23rd

PDC bytes—Dehammed Byte 13 to Byte 25

24th to 42nd

Raw status bytes

X/26, X/27, X/28, X/29, X/30, X/311

1st

Magazine number—Dehammed Byte 4

2nd

Row number—Dehammed Byte 5

3rd

Design code—Dehammed Byte 6

4th to 42nd

Raw data bytes

1 For X/26, X/28, and X/29, further decoding needs 24 × 18 hamming decoding. Not supported at present.

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