SNES_PWR = Bits 11111000 = Top 5 data pins on parport tied together
SNES_LAT = Bits 00000010 = Second data pin on parport
SNES_CLK = Bits 00000001 = First data pin on parport

_ = low, - = high

         Line 123    124    126    127    128    129    130    131
Pin 1: Power: -----------------------------------------------------
Pin 2: Clock: ----------------------------_______--------------____
Pin 3: Latch: _______-------_______________________________________
Pin 4:  Data:                      'B'                  'Y'
      Output: 0xf9   0xfb   0xf9          0xf8   0xf9          0xf8

Line 123: Supply power to the top 5 pins (tied together to hopefully
          provide enough current without blowing up your parallel
          port), keep clock high, keep latch low.
          0xf9 = 11111000 + 00000001
Line 124: Take latch high, which should make the controller read the
          value of all the switches (buttons) inside.
          0xfb = 11111000 + 00000010 + 00000001
Line 126: Take latch low, which should store the value of everything
          read above and have the results prepared for reading.
          0xf9 = 11111000 + 00000001
Line 127: Clock is high, so the first button ('B') is being sent on
          the data pin.  Read it.
Line 128: We're done reading this button, so we take clock low.
          0xf8 = 11111000
Line 129: We want the next button, so we take clock high.
          0xf9 = 11111000 + 00000001
Line 130: We read the bit currently being sent on the data pin (for
          the 'Y' button.)
Line 131: We've got it, take clock low.
          0xf8 = 11111000
          ...etc.