     $DC01/56321/CIA1+1:   Data Port Register B (Keyboard, Joystick, Paddles)

       +----------+---------------------------------------------------+
       | Bits 7-0 |   Read Keyboard Row Values for Keyboard Scan      |
       | Bit  7   |   Timer B Toggle/Pulse Output                     |
       | Bit  6   |   Timer A: Toggle/Pulse Output                    |
       | Bit  4   |   Joystick B Fire Button: 0 = Pressed             |
       | Bit  3   |   Joystick B Right: 0 = Pressed, or Paddle Button |
       | Bit  2   |   Joystick B Left : 0 = Pressed, or Paddle Button |
       | Bit  1   |   Joystick B Down : 0 = Pressed                   |
       | Bit  0   |   Joystick B Up   : 0 = Pressed                   |
       +----------+---------------------------------------------------+

       Joystick B is the one plugged into Port 1.

    Kernal-Reference:

     CMP $DC01   : $EAAE $F6BF
     CPX $DC01   : $F6CF
     LDA $DC01   : $E93D $EAAB $F6BC
     LDX $DC01   : $EA93 $F6CC