Patent ID: 7287098

Claim:
A control method for a main unit and an electronic device removably connected thereto, comprising: providing a register in the electronic device, the register having a write area and a read area for setting of codes of functions representing different types of devices and to be executed by the electronic device; providing an add-on register in the electronic device, the add-on register being coupled to the register through a system control circuit, the system control circuit being operable to supply a control signal for driving a memory controller connected to the register; writing the code of a function requested by the main unit in the write area of the register; and controlling, by the main unit, execution of the requested function based upon at least the code of the function read out from the read area, the step of controlling further comprising comparing the code of the function read out from the read area with the code of the function in the write area, determining that the function associated with the code written in the write area is installed in the electronic device if the comparison indicates a match, and determining that the function associated with the code written in the write area is not installed in the electronic device if the comparison does not indicate a match.