Tilemap

Tilemap

A screen mode similar to hardware text linked to the ULA modes which allows for either 40x32 or 80x32, 16-colour or 2-colour, 8x8 tiles.

Note that NextBASIC also has an older software tilemap, which operates quite differently from the hardware tilemap (sometimes called layer 3) described here. NextBASIC doesn't yet have commands to access hardware tilemap natively, although the techniques described here can be used with `REG` and manual memory control. And the software tilemap is not directly accessible to assembly language programs, although the IDE_TOKENISER and IDE_BASIC NextZXOS API calls can execute arbitrary BASIC commands.

The hardware tilemap is enabled using Tilemap Control Register ($6B / 107)

 bit 7: 0=disable tilemap, 1=enable tilemap
 bit 6: 0=40x32, 1=80x32
 bit 5: 0=attributes in tilemap, 1=no attributes in tilemap
 bit 4: 0=primary palette, 1=secondary palette
 bit 3: Select textmode (soft reset = 0)
 bit 2: reserved
 bit 1: 0=256 tile mode, 1=512 tile mode
 bit 0: 1=tilemap over ULA

The tilemap consists of two data areas: tile descriptions and an actual tilemap; both of which are located in 16k page 5

Tile Description

The tile description area is a contiguous list of tile descriptions starting at the location indicated by bits 5-0 of the value in Tile Definitions Base Address Register ($6F / 111).

Each tile description is a 32 byte block of 4-bit values describing the indices of each pixel of a tile in row major order.

In textmode, tiles are monochrome and take 8 bytes, making them essentially the same as ULA text chars and UDGs.

Tilemap

The tilemap begins at the location stored in bits 5-0 of Tilemap Base Address Register ($6E / 110).

This map either consists of either pairs of tile numbers and tile attributes, or a list of tile numbers. If no attributes are present (bit 5 of Nextreg $6B=1) then the attributes for all tiles come globally from Default Tilemap Attribute Register ($6C / 108).

In textmode, the second attribute byte and the global attriute lose the x mirror, y mirror and rotate, so bits 7-1 become a much larger palette offset that can take values between 0 and 127. The palette offset then points to one of 128 different paper/ink pairs in the palette. THe paper colour is at (palette offset * 2), and the ink colour is at ((palette offset * 2) + 1).

Tile Attribute

In 16 color mode:

 bits 7-4: palette offset
 bit 3: mirror X
 bit 2: mirror Y
 bit 1: Rotate
 bit 0: In 256-tile mode ULA over tilemap, in 512-tile mode bit 8 of tile number

In textmode:

 bits 7-1: palette offset
 bit 0: In 256-tile mode ULA over tilemap, in 512-tile mode bit 8 of tile number

Additional Registers

Clip Window Tilemap Register ($1B / 27)

 bits 7-0: Coord. of the clip window
 1st write = X1 position
 2nd write = X2 position
 3rd write = Y1 position
 4rd write = Y2 position
 The values are 0,159,0,255 after a Reset
 Reads do not advance the clip position

Tilemap Offset X MSB Register ($2F / 47)

 bits 7-2: Reserved (0)
 bits 1-0: MSB X Offset
 Meaningful Range is 0-319 in 40 char mode, 0-639 in 80 char mode

Tilemap Offset X LSB Register ($30 / 48)

 bits 7-0: LSB X Offset
 Meaningful range is 0-319 in 40 char mode, 0-639 in 80 char mode

Tilemap Offset Y Register ($31 / 49)

 bits 7-0: Y Offset (0-255)

Enhanced ULA Control Register ($43 / 67)

 bit 7: '1' to disable palette write auto-increment.
 bits 6-4: Select palette for reading or writing:
    000 = ULA first palette
    100 = ULA second palette
    001 = Layer 2 first palette
    101 = Layer 2 second palette
    010 = Sprites first palette 
    110 = Sprites second palette
    011 = Tilemap first palette
    111 = Tilemap second palette
 bit 3: Select Sprites palette (0 = first palette, 1 = second palette)
 bit 2: Select Layer 2 palette (0 = first palette, 1 = second palette)
 bit 1: Select ULA palette (0 = first palette, 1 = second palette)
 bit 0: Enable Enhanced ULA mode if 1 (0 after a reset)

ULA Control Register ($68 / 104)

 bit 7: 1 to disable ULA output
 bit 6: 0=select the ULA colour for blending in SLU modes 6 & 7
        1=select the ULA/tilemap mix for blending in SLU modes 6 & 7
 bits 5-1: Reserved (0)
 bit 0: 1=enable stencil mode when both the ULA and tilemap are enabled
           (if either are transparent the result is transparent otherwise the
            result is a logical AND of both colours)

More info

Article about Tilemap Mode