| 摘要 |
<p>A general-purpose input/output device that can be connected or disconnected without affecting other expansion units connected to a system bus. An expansion unit (800) including an electronic circuit (400) and a MOS switch (300) is connected to a system bus (BUS) through a connector having long and short pins. The expansion unit (800) has two power supply systems, i.e. a stable power supply system (250) and an unstable power supply system (260). Power is supplied from the stable power supply system (250) through a pair of long pins to the MOS switch (300) and to a high impedance holding circuit (350) so that the MOS switch (300) is definitely brought into a high impedance state when it is connected or disconnected, while the high impedance holding circuit (350) drives a switch control terminal inside the expansion unit so that power is supplied to the electronic circuit (400) from the unstable power supply system (250). The expansion unit avoids interference in signal transmission on the system bus and reduces influences of load fluctuation on a main power supply.</p> |
