      BRK                          BRK Force Break                          BRK

      Operation:  Forced Interrupt;                         N V - B D I Z C
                  PC + 2 to Stack, P to Stack               . . . 1 0 1 . .

      +----------------+-----------------------+---------+---------+----------+
      | Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
      +----------------+-----------------------+---------+---------+----------+
      |  Implied/Stack |   BRK                 |   $00   |    1    |    7     |
      +----------------+-----------------------+---------+---------+----------+
      1. A BRK command cannot be masked by setting I.
      2. Although even official documents say BRK uses implied addressing-mode,
         it is rather an immediate one, but the operand is thrown away. This is
         why PC+2 is pushed onto stack rather than PC+1. So, better use a NOP
         directly after BRK to avoid trouble.
      3. To be very precise: The B-flag is not set by BRK. It is rather set all
         the time, only when an external IRQ is recognized it will be cleared for
         some cycles, so you can distinguish between BRK and IRQ.