PURPOSE: To execute a high-speed processing by comparing command data to be transmitted with fixed value prepared in advance, inactivating the personal computer when they are equal, and realizing compatibility.

CONSTITUTION: This personal computer is composed of a microprocessor 10, controller 20, keyboard controller 30, buffer 40, logic circuit 50 and K/B 60. When the command data are issued from the microprocessor 10 to the K/B controller 30, the command data are stored in the latch storing means of the controller 20 and compared with the value of command data, which are prepared by a hardware as fixed value in advance, by a comparing means. Corresponding to the state of control bits in the command data, a control signal 100 of address lines 120 is generated and reported from the controller 20 to the logic circuit 50. Then, the signal is ANDed with a specified address 110 and outputted as the address line 120 of the system.