Keyboard

        R/W
Index   Mode  Description
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-00h    W     Low byte of keyboard output register (KB[0-7]) A write to this location
              starts keyboard precharge.
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-01h    W     Middle byte of keyboard output register (KB[8-15])
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-02h    W     High 6 bits of keyboard output register (KB[16-21])
              bits 0-5   KB[16-21]
              bits 6-7   unused
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-03h    W     A write to this location ends keyboard precharge.
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-00h    R     Low byte of keyboard input register (KB[0-7])
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-01h    R     Middle byte of keyboard input register (KB[8-15])
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-02h    R     High byte of keyboard input register (KB[16-21], KBI[22-23]))
              bits 0-5      KB[16-21]
              bits 6-7      KBI[22-23]
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-03h    R     bit 0      ON Key Pressed flag
              bits 1-7   unused
              Note: bit 0 will be set while the ON key is pressed and after it is
              released, reading this register after the ON key is released clears bit 0.
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