On an AND logic gate, how can you proven triggering a high when no input is recieved?
Answer:
Use "pull up" or "pull down" resistors to control the desired state of your inputs when there is no signal.
Pull up means connecting the input to Vcc by a large resistor.
Pull down means connecting the input to the ground by a large resistor.
Use a pull-down resistor.
This is generally a 1kohm resistor connected between the input and ground.
You should never leave unused inputs unconnected or you will get all sorts of strange effects. Set them to high or low logic level as appropriate by connecting them to +5V or ground through a resistor -- 10kohm is about right.
If you still have trouble with your logic circuits, remember that if you are clocking at above a few MHz you should decouple every chip with a small capacitor from +5V to ground placed physically close to the chip. This prevents activity on other chips feeding back through the supply rail, which can cause very puzzling effects. A 10nF ceramic will usually do the job.
With an AND gate or a NOR gate you can simply tie unused inputs to the nearest used input. For OR gates and NAND gates you definitely need pull-up or pull-down resistors.
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