# Skill: VIC-II Graphics, Screen, Characters, Sprites, and Raster

## Use this skill when

The task involves screen memory, colors, sprites, character sets, bitmap graphics, raster interrupts, scrolling, border/background, or VIC-II banking.

## Core registers

VIC-II base: `$D000` / `53248`.

| Decimal | Hex | Purpose |
|---:|---:|---|
| 53248-53263 | `$D000-$D00F` | Sprite X/Y coordinates |
| 53264 | `$D010` | High bits for sprite X positions |
| 53265 | `$D011` | Control register 1; vertical scroll, screen on, bitmap, raster bit 8 |
| 53266 | `$D012` | Raster line low byte |
| 53267 | `$D013` | Light pen X |
| 53268 | `$D014` | Light pen Y |
| 53269 | `$D015` | Sprite enable bits |
| 53270 | `$D016` | Control register 2; horizontal scroll, multicolor |
| 53271 | `$D017` | Sprite Y expansion |
| 53272 | `$D018` | Memory control: screen and character/bitmap pointers |
| 53273 | `$D019` | Interrupt flags |
| 53274 | `$D01A` | Interrupt enable |
| 53275 | `$D01B` | Sprite/background priority |
| 53276 | `$D01C` | Sprite multicolor enable |
| 53277 | `$D01D` | Sprite X expansion |
| 53278 | `$D01E` | Sprite-sprite collision |
| 53279 | `$D01F` | Sprite-background collision |
| 53280 | `$D020` | Border color |
| 53281 | `$D021` | Background color 0 |
| 53282-53284 | `$D022-$D024` | Extra background/multicolor registers |
| 53285-53286 | `$D025-$D026` | Sprite multicolor registers |
| 53287-53294 | `$D027-$D02E` | Sprite individual colors |

## Screen basics

Default screen RAM: `$0400` / `1024`.
Default color RAM: `$D800` / `55296`.
Screen is 40 columns x 25 rows = 1000 character cells.

Cell address:

```text
screen = 1024 + row * 40 + column
color  = 55296 + row * 40 + column
```

## Sprite basics

- Each sprite is 24 x 21 pixels.
- Each sprite pattern uses 64 bytes.
- Default sprite pointers are `$07F8-$07FF` / `2040-2047`.
- Pointer value = sprite data address / 64, within the active VIC bank.
- Enable sprites with `$D015` bits.

Example enable sprite 0 in BASIC:

```basic
POKE 53269,PEEK(53269) OR 1
```

## VIC-II bank rule

The VIC-II sees one 16K bank at a time. CIA #2 port A controls the video bank. All active screen RAM, character data, bitmap data, and sprite data must be visible inside the selected VIC bank.

## Character ROM copy warning

To copy character ROM from CPU-visible `$D000-$DFFF`, you must bank character ROM in and I/O out. Since I/O disappears during that window, disable interrupts briefly and restore banking immediately.

## Raster interrupt principles

- Set raster line in `$D012`; bit 8 is in `$D011`.
- Enable raster IRQ in `$D01A` bit 0.
- Acknowledge VIC interrupt by writing the relevant bit back to `$D019`.
- Chain or jump to the normal KERNAL IRQ handler unless replacing the system IRQ completely.

## Agent checklist

1. Give addresses in decimal and hex.
2. Preserve unrelated VIC register bits.
3. Note PAL/NTSC timing differences for raster work.
4. Keep sprite data inside active VIC bank.
5. For character/bitmap changes, explain `$D018` layout.