I can't grasp the concept of a pull-down resistor in microcontroller circuit. (See attachment) I realize that the purpose of a pull-down resistor is to keep the input P3 at a low state instead of floating when the switch is open; however, I cannot see why putting the 10k ohm resistor where it is would make any difference. If you do not have a resistor in that position, P3 would be connected to ground, (Vss) and it would be low anyway! I realize you need the resistor there when the button is pushed to prevent excessive current, but when the switch is open,, I don't get it??? (Vdd is at five volts.) Any help in explaining this would be appreciated.
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