An electronic device comprising a state machine is coupled between the ROM and its socket. When armed by an arming sequence, the device responds to an address from a microprocessor during a reset operation to modify the output of the ROM. The modified output causes a jump to a routine in RAM rather than a jump in an initialization routine in the ROM. This enables a user to change the microprocessor's addressing mode from protected to real without a complete initialization of the system. Arming of the device and reset of microprocessor is caused by a protected mode routine, and after reset the mircroprocessor processes a real mode routine.