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C64-screen-modes.md

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VIC II Screen Modes

*based on c64 Programmers Referance

Screen size is 40x25 char or 320 x 200 pixels $d011 bit 5 controls bitmap mode $d016 bit 4 controls multi color mode

Such that:

Screen Mode $d011 $d016
Hires text mode $1b $08
Multicolor text mode $1b $18
Hires bitmap mode $3b $08
Multicolor bitmap mode $3b $18
ECM text mode $5b $08
  1. Hires Text Mode:

This is the default mode
screen is filled by characters described by screen_ram ($0400)

Each bit on character rom represent 1 pixel
0 -> screen color: $d021
1 -> color ram

  1. Multicolor Text Mode

    bit pairs on character rom determines a pixel such that
    00 -> background #0 $d021
    01 -> background #1 $d022
    10 -> background #2 $d023
    11 -> color ram

  2. ECM Text Mode

    Gives more control over the background colors but limited to 64 chars.

    character code background color 00xxxxxx bg #0 $d021 01xxxxxx bg #1 $d022 10xxxxxx bg #2 $d023 11xxxxxx bg #3 $d024

  3. Hires Bitmap Mode

    instead of color_ram, screen_ram is now used for color information and charater_ram used to hold bitmap data

  4. Multicolor Bitmap Mode

    bit pairs represents pixel 00 -> bg #0 ($d021) 01 -> upper 4 bits of screen memory 10 -> lover 4 bits of creen memory 11 -> color nyble