VIC-II MEMORY

VIC-II Bank Reference & Memory Map

Even though RIFT64 frees you from writing raw assembly, your backend program still needs to understand the structure and constraints of the C64's VIC-II (Video Interface Chip). Use this memory map reference to design graphics offsets, custom character sets, bitmaps, and sprites inside the four 16KB hardware chunks.

1. Visual 64KB System Memory Map

This visual representation illustrates the entire 64KB RAM layout of the Commodore 64, ordered from high-memory (top) to low-memory (bottom), color-coded by architecture layers:

2. Active 16KB VIC-II Banks

The VIC-II chip can only access 16KB of RAM at once. The active bank is chosen using CIA 2 Register `$DD00` (bits 0 and 1):

3. Internal Offset Pointers (`$D018`)

VIC-II Register `$D018` defines where Screen Character RAM and Character Graphics RAM reside *within* the currently active 16KB bank:

4. Visual 16KB Bank Memory Allocations

Below is a comprehensive textual breakdown of how the memory layout is segmented inside the four physical 16KB VIC-II banks:

Bank 0 ($0000 - $3FFF) - System Default Bank

Bank 1 ($4000 - $7FFF) - High-Performance Free RAM

Bank 2 ($8000 - $BFFF) - System ROM Bank

Bank 3 ($C000 - $FFFF) - Code & Sprite Space

5. VIC-II Hardware Graphics Modes

• Standard Character Mode: Set `$D011` to `$1B` (BMM=0) and `$D016` to `$08` (MCM=0). Provides 40x25 character grid, 2 colors per cell (Bg & Fg).
• Multicolor Character Mode: Set `$D011` to `$1B` and `$D016` to `$18` (MCM=1). Character cells now use multicolor decoding, providing 4 colors per cell (fat pixels).
• Standard Bitmap Mode: Set `$D011` to `$3B` (BMM=1) and `$D016` to `$08`. High resolution 320x200 canvas, with 2 colors per 8x8 block.
• Multicolor Bitmap Mode: Set `$D011` to `$3B` (BMM=1) and `$D016` to `$18` (MCM=1). Multicolor 160x200 resolution, allowing up to 4 colors per 8x8 block.

6. Sprite Memory Structure (64-Byte Grid)

Each C64 hardware sprite is represented in memory as exactly 64 bytes. The pixel layout is 24 pixels wide by 21 pixels high, which translates to 3 bytes per horizontal line over 21 lines:

Line 0:  [Byte 0: %00111100] [Byte 1: %01111110] [Byte 2: %00111100]  (24 Pixels)
Line 1:  [Byte 3: %01111110] [Byte 4: %11111111] [Byte 5: %01111110]  (24 Pixels)
Line 2:  [Byte 6: %11111111] [Byte 7: %11111111] [Byte 8: %11111111]  (24 Pixels)
...
Line 20: [Byte 60]           [Byte 61]           [Byte 62]            (24 Pixels)
Padding: [Byte 63: Unused / Stardust Padding Byte]
                

7. Custom Character Set (8-Byte Font Grid)

The C64's custom character set glyphs are stored in memory as a series of 8-byte blocks. Each character in an 8x8 font grid is represented by exactly 8 consecutive bytes, where each byte dictates one horizontal pixel row:

Row 0:  . . X X X . . .   Binary: %00111000 → Hex: $38  (Row Value)
Row 1:  . X . . . X . .   Binary: %01000100 → Hex: $44  (Row Value)
Row 2:  X . . . . . X .   Binary: %10000010 → Hex: $82  (Row Value)
Row 3:  X X X X X X X .   Binary: %11111110 → Hex: $FE  (Row Value)
Row 4:  X . . . . . X .   Binary: %10000010 → Hex: $82  (Row Value)
Row 5:  X . . . . . X .   Binary: %10000010 → Hex: $82  (Row Value)
Row 6:  X . . . . . X .   Binary: %10000010 → Hex: $82  (Row Value)
Row 7:  . . . . . . . .   Binary: %00000000 → Hex: $00  (Row Value)
                

8. Official Commodore 64 Color Palette

Use these official C64 palette color codes (0-15 / $00-$0F) when sending color commands (like `K` and `Q` or sprite register values `CC`).