JPH0558289B

PURPOSE:To use an output bus in common between systems having a different power voltage by inserting a switch between a power supply and a bulk of CMOS transistors (TRs) of series connection forming a high impedance circuit. CONSTITUTION:The high impedance circuit is formed by N-channel and P- channel TRs 1, 2 connected respectively to a power terminal 3 and a ground terminal 4, and when the TRs 1, 2 are turned off, an output point X reaches a high impedance. Switches 31, 32 are provided between the power supply and the bulk of the TRs. In connecting a similar high impedance circuit to a common output bus,when the switches 31, 32 are turned off, even when the power voltage VCC differs, no diode due to the stray capacitance is formed to the TRs 1, 2 and no current flows to a low voltage power supply from the high voltage power supply via the common output bus line. Thus, the output bus is used in common between the systems using different power supply without hindrance.