Abstract: A data input controller which can set a keyboard to a key lock mode without affecting the operation state of a central processing unit (CPU). In the normal key input enable state, a keyboard encoder encodes a key input through the keyboard and sends the resultant data via a keyboard controller to the CPU. In this state, when a specific key combination is entered through the keyboard, the keyboard encoder detects it and sets the key lock mode. The encoded data corresponding to the subsequent key inputs is not sent to the keyboard controller. If a desired password is entered at this time, it is registered in RAM in the keyboard controller. The key lock mode is released when the registered password is entered.