Patent ID: 7091598

Claim:
An electronic circuit device, comprising: a microcomputer having a CPU; a random access memory; and a programmable device which implements a logic function in a programmable manner in accordance with logic definition data loaded in numerous memory cells, wherein each of said microcomputer, said random access memory and said programmable device is formed on a respective semiconductor chip, wherein the semiconductor chips are mounted on one side of a common substrate of a circuit board, wherein said common substrate has a plurality of external mounting pins on another side thereof being formed to directly connect to another circuit board, wherein said plurality of external mounting pins are adapted to connect to said programmable device, wherein said microcomputer includes a memory buffer, which is connected to said random access memory through an exclusive memory bus, said exclusive memory bus being formed on said common substrate without being connected to said external mounting pins, and wherein said memory buffer has an output buffer which is connected to said exclusive memory bus, said output buffer includes an output MOS transistor and an output impedance controlling MOS transistor which is coupled to said output MOS transistor, said output impedance controlling MOS transistor has its conduction impedance controlled by a control voltage which is put out from a control circuit.