logic gate (AND, OR, XOR, NOT, NAND, NOR, and XNOR)
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A logic gate is an elementary building block of a digitalcircuit. Most logic gates have two inputs and one output. At any given moment, every terminal is in one of the two binaryconditions low (0) or high (1), represented by different voltage levels. The logic state of a terminal can, and generally does, change often, as the circuit processes data. In most logic gates, the low state is approximately zero volts (0 V), while the high state is approximately five volts positive (+5 V).
There are seven basic logic gates: AND, OR, XOR, NOT, NAND, NOR, and XNOR.
The AND gate is so named because, if 0 is called "false" and 1 is called "true," the gate acts in the same way as the logical "and" operator. The following illustration and table show the circuit symbol and logic combinations for an AND gate. (In the symbol, the input terminals are at left and the output terminal is at right.) The output is "true" when both inputs are "true." Otherwise, the output is "false."
Pin-wise functioning of IC 555 timer
Pin-1: It is the GROUND PIN of the IC. The negative terminal of DC power supply or battery is connected to this pin. Here note that IC555 works always on single rail power supply and NEVER on dual power supply, unlike operational amplifiers.
Also note that this pin should be connected directly to ground and NOT through any resistor or capacitor. If done so, the IC will not function properly and may heat up and get damaged. This happens because all the semiconductor blocks inside the IC will be raised by certain amount of stray voltage and will damage the IC. Refer the block diagram of the IC for more details. For more details read elaborate collection of FAQ on this IC.