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Enhance documentation on screen modes and memory layout #280

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be32a5f
Enhance documentation on screen modes and memory layout
indigodarkwolf Jan 11, 2026
2475f15
Enhance text modes memory layout description
indigodarkwolf Jan 11, 2026
1029fb0
Enhance BASIC.md with references to relevant commands from SCREEN.
indigodarkwolf Jan 11, 2026
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24 changes: 24 additions & 0 deletions X16 Reference - 04 - BASIC.md
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Expand Up @@ -1520,6 +1520,30 @@ The above example overwrites an existing file on drive 9, which would be a Commo

For a list of supported modes, see [Chapter 3: Editor](X16%20Reference%20-%2003%20-%20Editor.md#chapter-3-editor). The value of -1 toggles between modes $00 and $03.

To edit text on the screen, refer to the following commands:
* [CHAR](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#char)
* [COLOR](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#color)
* [LOCATE](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#locate)
* [POS](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#pos)
* [TATTR](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#tattr)
* [TDATA](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#tdata)
* [TILE](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#tile)

To edit bitmap data in screen mode $80, refer to the following commands:
* [FRAME](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#frame)
* [LINE](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#line)
* [OVAL](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#oval)
* [PSET](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#pset)
* [RECT](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#rect)
* [RING](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#ring)

Direct writing of the VERA's memory can be performed via [VPOKE](https://github.com/X16Community/x16-docs/blob/master/X16%20Reference%20-%2004%20-%20BASIC.md#vpoke).

Details about programming for the VERA video adapter can be found in [Chapter 9: VERA Programmer's Reference](X16%20Reference%20-%2009%20-%20VERA%20Programmer's%20Reference.md). In particular, please refer to the sections on [VRAM Address Space Layout](X16%20Reference%20-%2009%20-%20VERA%20Programmer's%20Reference.md#vram-address-space-layout) and [Tile mode 1 bpp (16 color text mode)](X16%20Reference%20-%2009%20-%20VERA%20Programmer's%20Reference.md#tile-mode-1-bpp-16-color-text-mode). All text modes use Tile mode 1 bpp (16 color text mode), with 128 tiles per line and 64 lines, even though the display will not show the entire range at once.

The video memory for all text modes start at VERA bank 1, address $B000. (e.g. `VPOKE 1, $B000, 0`).
For mode $80, bitmap memory starts at VERA bank 0, address $0000. (e.g. `VPOKE 0, $0000, 0`).

**EXAMPLE of SCREEN Statement:**

```BASIC
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