Power Pad

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The Power Pad exercise mat for the Nintendo Entertainment System has twelve sensors arranged in a 3x4 grid, which the player steps on to control the action on the screen.

The Power Pad can be used in either controller port, though most games will only allow you to use it in controller port #2, leaving port #1 for a standard controller used for navigating through options.

          |                        |
,---------+---------.    ,---------+---------.
| POWER PAD  side B |    | POWER PAD  side A |
|  (1) (2) (3) (4)  |    |      (O) (O)      |
|                   |    |                   |
|  (5) (6) (7) (8)  |    |  (O) (X) (X) (O)  |
|                   |    |                   |
|  (9) (10)(11)(12) |    |      (O) (O)      |
|                   |    |                   |
`-------------------'    `-------------------'

The sensors are spaced at 252 mm across by 285 mm front and back.

Most games used side B, with the numbers on top. A few games turned the pad over to side A, whose markings lack numerals and lack markings for spaces 1, 4, 9, and 12 entirely (but they still send a signal). There is a third possible configuration, which no official game used, but which may be useful for homebrew dance simulation games in the style of Dance Dance Revolution: side B rotated 90 degrees anticlockwise, placing sensors 4, 8, and 12 toward the display.

| ,---------------.           | ,---------------.
| |  SIDE B       |           | |  SIDE DDR     |
| |  (4) (8) (12) |           | | (Sel)    (St) |
| |               |           | |               |
| |  (3) (7) (11) |    ____   | |  (X) (U) (O)  |
`-+               |    ____   `-+               |
  |  (2) (6) (10) |             |  (L)     (R)  |
  |               |             |               |
  |  (1) (5) (9)  |             |      (D)      |
  |               |             |               |
  `---------------'             `---------------'

Hardware interface

Input ($4016 write)

7  bit  0
---- ----
xxxx xxxS
        |
        +- Controller shift register strobe

Writing 1 to this bit will record the state of each button. Writing 0 afterwards will allow the buttons to be read back, two at a time.

Output ($4016/$4017 read)

7  bit  0
---- ----
xxxH Lxxx
   | |
   | +---- Serial data from buttons 2, 1, 5, 9, 6, 10, 11, 7
   +------ Serial data from buttons 4, 3, 12, 8 (following 4 bits read as H=1)

The first 8 reads will indicate which buttons are pressed (1 if pressed, 0 if not pressed); all subsequent reads will return H=1 and L=1.

Remember to save both bits that you get from each read. If you're playing samples, beware of bit deletions.

Family Trainer Mat

The Famicom's version of the Power Pad looked similar, but had an entirely different protocol that took advantage of the greater number of digital outputs on the Famicom expansion port:

Input ($4016 write)

7  bit  0
---- ----
xxxx xABC
      |||
      ||+-- 1: Ignore bottom row, 0: include bottom row (buttons 9-12)
      |+--- 1: Ignore middle row, 0: include middle row (buttons 5-8)
      +---- 1: Ignore top row, 0: include top row (buttons 1-4)

Output ($4017 read)

7  bit  0
---- ----
xxxD EFGx
   | |||
   | ||+-- right-most column (buttons 4,8,12)
   | |+--- right-center column (buttons 3,7,11)
   | +---- left-center column (buttons 2,6,10)
   +------ left-most column (buttons 1,5,9)

If a button is pressed in the currently selected rows, then the output returns 0. If no button is pressed, the output for that column is 1.

The Famicom must manually scan the matrix; additionally it seems that there are quite large parasitic capacitances so you may need to wait a whole millisecond before going on to the next row.

It is not known whether the Family Trainer mat has included diodes for n-key-rollover, or whether pressing buttons on three corners of a square will cause a ghost press on the last corner.

Programs