Page function and coding
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In a Basic Level 1 Teletext page (LOP), packets X/1–24 contain text and mosaic graphics encoded as 7 data bits and 1 odd parity bit. Teletext pages may also be used to carry data not for direct display however, and may employ alternative encoding methods.
Twelve page functions are defined by the enhanced teletext specification[1] and are communicated to a decoder in packet X/28/0 using the values shown in the following table. AIT, MPT, and MPT-EX functions all relate to navigation via Table Of Pages.
| Page Function | |
| 0 | Basic Level 1 Teletext page (LOP) |
| 1 | Databroadcast page |
| 2 | Global Object definition page (GPOP) |
| 3 | Normal Object definition page (POP) |
| 4 | Global DRCS downloading page (GDRCS) |
| 5 | Normal DRCS downloading page (DRCS) |
| 6 | Magazine Organization table (MOT) |
| 7 | Magazine Inventory page (MIP) |
| 8 | Basic TOP table (BTT) |
| 9 | Additional Information Table (AIT) |
| 10 | Multi-page table (MPT) |
| 11 | Multi-page extension table (MPT-EX) |
In addition to the page function, packet X/28/0 also defines the encoding scheme used by packets X/1–25.
| Page Coding | |
| 0 | All bytes encode 7 data bits and 1 odd parity bit. |
| 1 | All bytes encode 8 data bits. |
| 2 | In each packet, one Hamming 8/4 coded byte, followed by thirteen Hamming 24/18 coded triplets. |
| 3 | All bytes Hamming 8/4 coded. |
| 4 | In each packet, eight Hamming 8/4 coded bytes, followed by twelve bytes encoding 7 data bits and 1 odd parity bit. The remaining twenty bytes repeat the same pattern. |
| 5 | In each packet, one Hamming 8/4 coded byte which defines the coding of the remaining 39 bytes of the packet using the first five entries in this table. |
- ↑ ETS 300 706 chapter 9.4.2.1