| 摘要 |
<p>A keyboard interface is disclosed which, when a keyboard matrix (23) and an LED driver IC (19) are connected to a multi- function CPU (11), by outputting a scan signal and reading out a return signal through a bus line (17), can reduce the number of pins to its minimum and thus can increase pins having different functions. A printer interface is also disclosed which, when a printer is connected to a multi-function CPU, with addition of a date register, can increase the functions of the multi-function CPU under the limited number of pins by specifying a level mode or a printer strobe mode. The keyboard and printer interfaces are respectively capable of expanding the functions of the multi-function CPU (11) further by providing a port for requesting an interrupt as well as a register having an enable bit to inhibit such interrupt. The interfaces, when the functions of the multi-function CPU are further expanded, are adapted to be controllable systematically so as to prevent confusion by providing within the CPU a port to indicate the ID number of LSIs.</p> |
