![2.11.66 VDP TTX Filter And Mask Registers](/images/new-backgrounds/166612/166612137x1.webp)
Functional Description
2.11.66 VDP TTX Filter And Mask Registers
Subaddress | B1h | B2h | B3h | B4h | B5h | B6h | B7h |
| B8h | B9h | BAh |
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Default | 00h | 00h | 00h | 00h | 00h | 00h | 00h |
| 00h | 00h | 00h |
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Subaddress |
| 7 |
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| 6 | 5 |
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B1h |
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| Filter 1 mask 1 |
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| Filter 1 pattern 1 |
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B2h |
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| Filter 1 mask 2 |
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| Filter 1 pattern 2 |
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B3h |
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| Filter 1 mask 3 |
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| Filter 1 pattern 3 |
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B4h |
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| Filter 1 mask 4 |
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| Filter 1 pattern 4 |
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B5h |
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| Filter 1 mask 5 |
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| Filter 1 pattern 5 |
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B6h |
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| Filter 2 mask 1 |
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| Filter 2 pattern 1 |
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B7h |
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| Filter 2 mask 2 |
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| Filter 2 pattern 2 |
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B8h |
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| Filter 2 mask 3 |
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| Filter 2 pattern 3 |
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B9h |
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| Filter 2 mask 4 |
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| Filter 2 pattern 4 |
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BAh |
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| Filter 2 mask 5 |
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| Filter 2 pattern 5 |
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For an NABTS system, the packet prefix consists of five bytes. Each byte contains 4 data bits (D[3:0]) interlaced with 4 Hamming protection bits (H[3:0]):
Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
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D[3] | H[3] | D[2] | H[2] | D[1] | H[1] | D[0] | H[0] |
Only data portion D[3:0] from each byte is applied to a teletext filter function with corresponding pattern bits P[3:0] and mask bits M[3:0]. The filter ignores the Hamming protection bits.
For WST system (PAL or NTSC), the packet prefix consists of two bytes. The two bytes contain three bits of magazine number (M[2:0]) and five bits of row address (R[4:0]), interlaced with eight Hamming protection bits H[7:0]:
Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
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R[0] | H[3] | M[2] | H[2] | M[1] | H[1] | M[0] | H[0] |
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R[4] | H[7] | R[3] | H[6] | R[2] | H[5] | R[1] | H[4] |
The mask bits enable filtering using the corresponding bit in the pattern register. For example, a 1 in the LSB of mask 1 means that the filter module must compare the LSB of nibble 1 in the pattern register to the first data bit on the transaction. If these match, then a true result is returned. A 0 in a bit of mask means that the filter module must ignore that data bit of the transaction. If all 0s are programmed in the mask bits, then the filter matches all patterns returning a true result (default 00h).
TVP5147M1PFP | 61 |