clock signal clk and change the enable signal ebl1 to the inactive level however the status change from the loaded state to the unloaded state is not detectable the behavior of floppy disk controller 31 with reference to fig6 is described as follows assuming now that the floppy disk controller 31 is in the active mode the central processing unit 21a supplies the selecting signal sel indicative of the floppy disk driver unit 22 to the output port 21e at times t21 and t22 and the selecting signal sel is transferred through the or gate or1 to the floppy disk driver unit 22 the floppy disk fpy is still loaded in the floppy disk driver unit 22 at times t21 and t22 and the status signal sts indicative of the loaded state is supplied from the floppy disk driver unit 22 to the input port 21f the input port 21f latches the status signal sts in response to the latch control signal ltc and the status signal sts is transferred to the central processing unit 21a the central processing unit 21a compares the current status of the floppy disk driver unit 22 with the previous status and acknowledges that no status change takes place for this reason the interrupt request signal int is not produced at times t21 and t22 the central processing unit 21 a supplies the selecting signal sel indicative of the floppy disk driver unit 22 to the output port 21e at time t23 again and the selecting signal sel is transferred through the or gate or1 to the floppy disk driver unit 22 a user has already removed the floppy disk fpy from the floppy disk driver unit 22 before time t23 and the.