Tilemap Control Register
| Number | $6B |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | Controls Tilemap mode. |
| Bit | Function |
|---|---|
| 7 | 1 to enable the tilemap |
| 6 | 0 for 40x32, 1 for 80x32 |
| 5 | 1 to eliminate the attribute entry in the tilemap |
| 4 | palette select (0 = first Tilemap palette, 1 = second) |
| 3 | enable "text mode" |
| 2 | Reserved, must be 0 |
| 1 | 1 to activate 512 tile mode (bit 0 of tile attribute is ninth bit of tile-id) 0 to use bit 0 of tile attribute as "ULA over tilemap" per-tile-selector |
| 0 | 1 to enforce "tilemap over ULA" layer priority |
Bits 7 & 6 enable the tilemap and select resolution.
Bit 5 changes the structure of the tilemap so that it contains only 8-bit tilemap-id entries instead of 16-bit tilemap-id plus tile-attribute entries.
If 8-bit tilemap is selected, the tilemap contains only tile numbers and the attributes are taken from Default Tilemap Attribute Register ($6C).
Bit 4 selects one of two tilemap palettes used for final colour lookup.
Bit 3 enables "text mode" where the tile-graphic is defined as 1-bit B&W bitmap (same as UDG = User Defined Graphic characters on original ZX Spectrum) => one tile needs only 8 bytes to define graphics. The tile-map data are also interpreted differently, the associated flag byte is 7:1 split, the bottom bit 0 being still "ULA over Tilemap" or "ninth bit of tile number", but the top 7 bits are extended palette offset. The transparency is then checked against the Global Transparency Register ($14) colour (after the colour lookup in the palette), not against the four bit Tilemap transparency colour-index.
Bit 1 enables the 512-tile-mode when the tile attribute (either global in Default Tilemap Attribute Register ($6C) or per tile in map data) contains ninth bit of tile-id value. In this mode the tiles are drawn under ULA pixels, unless bit 0 is used to force whole Tilemap over ULA.
Bit 0 can enforce Tilemap over ULA either in 512-tile-mode, or even override the per-tile bit selector from tile attributes. If zero, the Tilemap priority is either decided by attribute bit or in 512-tile-mode it is under ULA.