Patent ID: 7371687

Claim:
An electronic circuit semiconductor device, a microcomputer including a CPU formed on a first chip; and a memory unit formed on a second chip, wherein said first chip and second chip are formed on one side of a common substrate of a board, wherein said common substrate has a plurality of external pins for connecting to another board, wherein said plurality of external pins are connected to said first chip, wherein said microcomputer includes a buffer unit for connecting to said memory unit via a memory bus, wherein said memory bus is formed on said common substrate without connecting to said external pins, wherein said buffer unit has an output buffer unit for connecting to said memory bus, wherein said output buffer unit includes an output transistor and an output impedance controlling transistor for connecting in series to said output transistor, and an output pin which is connected in series to said output transistor and said output impedance controlling transistor, and wherein said output impedance controlling transistor has its conduction impedance controlled by receiving on said gate electrode thereof a control voltage which is put out from a voltage generation unit.