![]() ![]() ![]() Just as NOR is an inverted OR, NAND is an inverted AND. Consider an interlock system with two inputs that will only allow the system to start if both interlocks are closed (0), and this is an example of a NOR gate. It can be thought of as an OR gate whose output promptly runs through a NOT gate. If the operator tries to turn on a second one, they both turn off.Ī NOR gate is simply the inverted OR gate. Suppose there is a device that has two high current heaters, but only one should run at a time. ![]() It does not matter which one, but only one is true. An Exclusive-OR (XOR) gate is true if and only if one input is true. Think back to every B nuclear war movie where two people have to turn keys to launch the missile - this is an example of an AND gate. An AND gate’s output is true if and only if all inputs are true. These buttons can be strung together as a cascade of OR gates.Įven though common language uses AND and OR interchangeably, they are not interchangeable. Consider a piece of equipment with multiple “emergency stop” buttons it doesn’t matter which one is pressed, and only one needs to be pressed to stop the device. If either input signal is true, the output is true. Because they only have one input, their truth table is very simple:Īn OR gate looks at two inputs. In other words, if it is fed a true signal, it will output a false signal and vice-versa. Not gateĪ NOT gate, sometimes called an INVERT, simply swaps an input’s state. Thoughtful planning can use these two gates to create some of the other types. In reality, sequences of these gates can be combined to create other gates, as NAND and NOT gates are very common in semiconductor chips, based on the device physics. There are seven basic types of logic gates, and for the purposes of this discussion, only one or two inputs and one output are required for each gate. They evaluate the inputs and, based on the gate, determine whether the output is true or false. Logic gates are methods to force an output based on inputs. Each of these inputs will have an output that corresponds to an output. For example, in the 4-bit system, the table would start with 0000 (0) up to 1111 (15). To do this, count in binary from zero to the one less than the number of states. Once the number of states is known, build a table where each row is a possible input. For example, a 4-bit system would have 16 possible input combinations (states), where each bit could be a 1 or 0. To set up a truth table, first evaluate how many inputs are available. Truth tablesĪ truth table is a way to organize and predict the output of a Boolean Logic circuit for all possible input states. Enter Boolean Logic, where logical statements are applied to inputs to control an output. In order to make a computer do anything useful, such as math, graphics, control operations or surf the net, multiple bits must be combined, and decisions must be made based on the status of all of these bits. ![]()
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