ADV7180
Data Sheet
I2C READBACK REGISTERS
WST_PKT_DECODE_DISABLE, Disable Hamming
Decoding of Bytes in WST, Address 0x60[3], User Sub Map
Teletext
Setting WST_PKT_DECODE_DISABLE to 0 enables hamming
decoding of WST packets.
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.
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:
TTXT_AVL, Teletext Detected Status, Address 0x78[7],
User Sub Map, Read Only
Input hamming coded byte: {D3, P3, D2, P2, D1, P1, D0, P0}
(bits in decoded order)
When TTXT_AVL is 0, teletext was not detected.
When TTXT_AVL is 1, teletext was detected.
WST Packet Decoding
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
Output Data Bits
in Nibble
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.
E[1:0] Error Information
00
01
10
11
No errors detected
Error in P4
Double error
Okay
Okay
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
Row number—Dehammed Byte 5
Page number—Dehammed Byte 6
Page number—Dehammed Byte 7
Control bytes—Dehammed Byte 8 to Byte 13
Raw data bytes
2nd
3rd
4th
5th to 10th
11th to 42nd
1st
Text Packets (X/01 to X/25)
Magazine number—Dehammed Byte 4
Row number—Dehammed Byte 5
Raw data bytes
2nd
3rd to 42nd
1st
2nd
3rd
4th to 10th
11th to 23rd
24th to 42nd
1st
2nd
3rd
4th to 10th
11th to 23rd
24th to 42nd
1st
2nd
3rd
4th to 42nd
8/30 (Format 1) Packet
Design Code = 0000 or 0001
UTC
Magazine number—Dehammed Byte 4
Row number—Dehammed Byte 5
Design code—Dehammed Byte 6
Dehammed initial teletext page, Byte 7 to Byte 12
UTC bytes—Dehammed Byte 13 to Byte 25
Raw status bytes
8/30 (Format 2) Packet
Design Code = 0010 or 0011
PDC
Magazine number—Dehammed Byte 4
Row number—Dehammed Byte 5
Design code—Dehammed Byte 6
Dehammed initial teletext page, Byte 7 to Byte 12
PDC bytes—Dehammed Byte 13 to Byte 25
Raw status bytes
X/26, X/27, X/28, X/29, X/30, X/311
Magazine number—Dehammed Byte 4
Row number—Dehammed Byte 5
Design code—Dehammed Byte 6
Raw data bytes
1 For X/26, X/28, and X/29, further decoding needs 24 × 18 hamming decoding. Not supported at present.
Rev. G | Page 62 of 120
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