PURPOSE: To obtain an easy-control terminal equipment by providing a means of enabling both microcomputers for modulation and demodulation processing and main-system control to read and write the contents of an external data memory.

CONSTITUTION: When a microcomputer 2 for modulation and demodulation outputs a bus-line switching command, two upper-side chips 6 for a bus driver (for control line connection of microcomputer 2 for modulation and demodulation processing) are unselected, and two lower-side chips 6' (for bus line connection of main system microcomputer 1) are selected. When the microcomputer 1 performs the reading and writing of an external data memory, a read/write strope is outputted to the external data memory 5, so that the microcomputer 1 is capable of reading and writing. At this time, the microcomputer 2 never disturbs the reading/writing processing of the microcomputer 1 because no read/write strobe is supplied to the memory 5.