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  1. DESKTOP x1k1
  2.                                 ╔═════════════════╗
  3.                                 ║     SHIFTER     ║
  4.                                 ║ bit assignments ║
  5.                                 ╚═════════════════╝
  6.                                  Atari SHIFTER
  7.               ┌─────────────────┐
  8.               │ SYNChronization │     b9=frequency (synchronization=internal)
  9.               │                 │        -:             (resolution=high)
  10.               │                 │                         frequency=71 Hz
  11.               │                 │                            screen=501 lines
  12.               │                 │                              line=28 µs
  13.               │                 │                    display enable=line 36 &
  14.               │                 │                                   col. 0 µs
  15.               │                 │        0:             (resolution=medium/low)
  16.               │                 │                         frequency=60 Hz
  17.               │                 │                            screen=263 lines
  18.               │                 │                              line=63.5 µs
  19.               │                 │                    display enable=line 35 &
  20.               │                 │                                   col. 6.5 µs
  21.               │                 │        1:             (resolution=medium/low)
  22.               │                 │                         frequency=50 Hz
  23.               │                 │                            screen=313 lines
  24.               │                 │                              line=64 µs
  25.               │                 │                    display enable=line 48/64 &
  26.               │                 │                                  =col. 7 µs
  27.               │                 │     b8=synchronization
  28.               │                 │        0:internal
  29.               │                 │        1:external
  30.               └─────────────────┘
  31.                    ┌────────────┐
  32.                    │ RESolution │  b9-b8=resolution
  33.                    │            │        00:low
  34.                    │            │        01:medium
  35.                    │            │        10:high
  36.                    └────────────┘
  37.                    ┌────────────┐
  38.                    │ Video Base │[b23-b8]=video base
  39.                    └────────────┘
  40.                 ┌───────────────┐
  41.                 │ Video Counter │[b23-b0]=video counter
  42.                 │               │         (1 word read each 500 ns)
  43.                 │               │         (when display enable)
  44.                 │               │         (without wait state for MC68000)
  45.                 └───────────────┘
  46.                ┌────────────────┐
  47.                │ Color Register │ b10-b8=[b2-b0]=red   level
  48.                │                │  b6-b4=[b2-b0]=green level
  49.                │                │  b2-b0=[b2-b0]=blue  level
  50.                │                │              (resolution=high   CR0b0=Ink    )
  51.                │                │              (                        0:white)
  52.                │                │              (                        1:black)
  53.                │                │              (resolution=medium CR0-CR3  used)
  54.                │                │              (resolution=low    CR0-CR15 used)
  55.                └────────────────┘
  56.