Fundamental Characteristics of Logic Gates
As the name reveals, a CMOS gate, is a “gate" or a passage (to electrons) that may be opened or closed by providing certain well-defined input instructions. These instructions are specific to each type of gate and can be found through their Truth Tables.
The most important and identifiable feature of these gates is that they will not respond to any intermediate values or levels of voltages. Any voltage below 3 volts (approx.) will be taken as a zero voltage or logic “0" and anything above it, a positive or logical “1". This is the only fundamental “language" that a logic gate understands, and that’s what makes them invariably accurate.
A typical CMOS gate basically comprises of an input and an output. The output is the function of its input and will respond to it as per its particular specifications. For example, the most preliminary form of such a gate is an “inverter" or the NOT gate. As the name suggests, the function of this particular gate is to invert or produce exactly the opposite result to that of its input status, i.e. if a positive voltage is applied to its input, the output will be a negative and vice versa.
Please note that the specific symbols of the various types of gates are just for recognizing purposes and for ease of their use in the schematics (nobody has cut through an IC to actually see how a gate looks), so don’t get confused by their symbolic appearances.
An IC may comprise many digital logic gates in one package (for example, the IC 4049 consists of 6 NOT gates), but in a schematic diagram these gates may be shown scattered all over, individually wired into separate circuits. Since all gates are identical, taking the help of the datasheet, you may just confirm the pin outs of the gates and connect them as shown in the particular schematic while constructing a circuit. You don’t have to bother regarding their serial number or placements.