PURPOSE: To obtain a microcomputer expansion controlling circuit omitting an exclusive terminal for expansion control by providing a titled circuit with two expansion controlling terminals processing two-way data and controlling the state of said terminals by a switching circuit.
CONSTITUTION: If the expansion controlling terminals 2-1, 2-2 are released when the microcomputer is used as a single chip microcomputer, latches 13W16 are kept at the high level. When an input or output instruction is executed, IN or OUT is turned to the high level, and when a corresponding port address is specified, an input or output is executed between an I/O port/data bus 3 and a data bus DB or a port latch. In case of an expansion mode, the terminals 2-1, 2-2 are kept at the low level. Consequently, a clock timing period in which the terminals 2-1, 2-2 are to be kept at the low level determines the operation mode out of plural ones.
TANIGAWA YUUJI
UEDA KATSUHIKO
SAKAO TAKASHI
Next Patent: METHOD FOR CONTROLLING TRANSFER OF DATA