Method and apparatus for overriding a ROM routine in response to

Details Method and apparatus for overriding a ROM routine in response to Method and apparatus for overriding a ROM routine in response to

1987-10-23

1991-05-21

Anderson, Lawrence E.

Boots, shoes, and leggings

3642802, G06F 936

Patent

active

050180622

ABSTRACT:
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.

REFERENCES:
patent: 4736290 (1988-04-01), McCallion
patent: 4779187 (1988-10-01), Letwin
patent: 4849875 (1989-07-01), Fairman et al.
patent: 4928237 (1990-05-01), Bealkowski et al.
Microprocessors and Microcomputer Development Systems, Designing Microprocessor-Based Systems, by Rafiquzzama, pp. 48-64, 1984.

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