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  1. DESKTOP x1k1
  2.                                 ╔═════════════════╗
  3.                                 ║  GI AY-3-8910   ║
  4.                                 ║ bit assignments ║
  5.                                 ╚═════════════════╝
  6.                                  General Instruments AY-3-8910
  7.                                  Programmable Sound Generator
  8.            ┌────────────────────┐
  9.            │ Selection Register │ b11-b8=[b3-b0]=selected register
  10.            └────────────────────┘
  11.       ┌─────────────────────────┐
  12.       │ PERiod of channel A/B/C │[b11-b0]=period of channel A/B/C
  13.       │                         │         unit=8 µs
  14.       └─────────────────────────┘
  15.               ┌─────────────────┐
  16.               │ PERiod of NOISE │ b12-b8=[b4-b0]=period of noise
  17.               │                 │                unit=8 µs
  18.               └─────────────────┘
  19.                     ┌───────────┐
  20.                     │ SELECTion │    b15=port B
  21.                     │           │        0:input
  22.                     │           │        1:output
  23.                     │           │    b14=port A
  24.                     │           │        0:input
  25.                     │           │        1:output
  26.                     │           │    b13=noise on channel C
  27.                     │           │        0:yes
  28.                     │           │        1:no
  29.                     │           │    b12=noise on channel B
  30.                     │           │        0:yes
  31.                     │           │        1:no
  32.                     │           │    b11=noise on channel A
  33.                     │           │        0:yes
  34.                     │           │        1:no
  35.                     │           │    b10=channel C
  36.                     │           │        0:selected
  37.                     │           │        1:unselected
  38.                     │           │     b9=channel B
  39.                     │           │        0:selected
  40.                     │           │        1:unselected
  41.                     │           │     b8=channel A
  42.                     │           │        0:selected
  43.                     │           │        1:unselected
  44.                     └───────────┘
  45.    ┌────────────────────────────┐
  46.    │ AMPlitude of channel A/B/C │    b12=envelope
  47.    │                            │        0:no
  48.    │                            │        1:yes
  49.    │                            │ b11-b8=[b3-b0]=amplitude of channel A/B/C
  50.    │                            │                logarithmic law: n+1=SQR(2)*n
  51.    └────────────────────────────┘
  52.            ┌────────────────────┐
  53.            │ PERiod of ENVelope │[b15-b0]=period of envelope
  54.            │                    │         unit=128 µs
  55.            └────────────────────┘
  56.                      ┌──────────┐
  57.                      │ ENVelope │ b10-b8=[b2-b0]=envelope
  58.                      │          │                000:\\\\\\\\
  59.                      │          │                001:\_______
  60.                      │          │                010:\/\/\/\/
  61.                      │          │                011:\-------
  62.                      │          │                100:////////
  63.                      │          │                101:/-------
  64.                      │          │                110:/\/\/\/\
  65.                      │          │                111:/_______
  66.                      └──────────┘
  67.                        ┌────────┐
  68.                        │ PORT A │    b14=general purpose output            (NOT)
  69.                        │        │    b13=parallel port strobe              (NOT)
  70.                        │        │    b12=serial port data terminal ready   (NOT)
  71.                        │        │    b11=serial port request to send       (NOT)
  72.                        │        │    b10=disk B
  73.                        │        │        0:selected
  74.                        │        │        1:unselected
  75.                        │        │     b9=disk A
  76.                        │        │        0:selected
  77.                        │        │        1:unselected
  78.                        │        │     b8=disk side
  79.                        │        │        0:side 1
  80.                        │        │        1:side 0
  81.                        └────────┘
  82.                        ┌────────┐
  83.                        │ PORT B │  b7-b0=parallel port data
  84.                        └────────┘
  85.