Arkanoid controller

The Arkanoid Vaus controller was included with the Arkanoid game, and is only used for this game and Chase HQ. It has an control knob connected to a potentiometer and a single fire button. Under a small black plastic cover is another potentiometer to adjust the control knob's range.

            ,--------------------------------------.   |
            |                  %%                  |   |
            |   ,---.          %%                % |   |
            |  /     \         %%         ,-.   %% |   |
 Control  ->| |       |        %%        (   )  %% |<- Fire button
   knob     |  \     /         %%         `-'   %% |   |    
            |   `---'          %%                % |==/
Adjustment->|     ()           %%                  |
   screw    `--------------------------------------'

The Famicom version of this controller uses D1 (Famicom) on both ports. The NES version uses D3 and D4, usually in port 2 ($4017). The controller will not work in a Four Score.

Input ($4016 write)

7  bit  0
---- ----
xxxx xxxS
        |
        +- Control knob shift register strobe

Writing 1 to this bit will record the state of the control knob. Writing 0 afterwards will allow the position to be read back.

The analog to digital conversion takes about 7 ms, so strobing too fast will return bad data, especially at the right side of the range. A function that reads the controller multiple times in a row to avoid DPCM glitches may not work. Instead, check for spurious accelerations, where the second difference x_t - 2x_{t - 1} + x_{t - 2} exceeds about eight units.

Output ($4016/$4017 read)

Famicom:

$4016:
7  bit  0
---- ----
xxxx xxBx
       |
       +-- Fire button (1: pressed)

$4017:
7  bit  0
---- ----
xxxx xxDx
       |
       +-- Serial control knob data

NES:

7  bit  0
---- ----
xxxD Bxxx
   | |
   | +---- Fire button (1: pressed)
   +------ Serial control knob data

Button status is returned in D3, and does not need to be latched. However, making sure it reads the same way eight times is a good way to distinguish it from a Power Pad, and reading it several times during a frame should distinguish it from the light sensor of a Zapper.

Control knob data is returned in D4, MSB first. The data is also inverted. The whole range is about 180 degrees, and returned in $A0 steps.

Variations in the analog to digital and pot physical range can vary the result slightly. With the trim pot at minimum the range returned is $0D-$AD. With the trim pot at maximum the range returned is $5C-$FC.

The Arkanoid game expects the range to be $54-$F4; the manual explains how to adjust the trimpot. New games can work at any trim pot setting by storing the maximum and minimum values seen during a play session and assuming values within ±80 units of the center of this range.

Test ROMs

• Vaus Test shows adaptation to trimpot setting, repeated read rate, and first and second differences