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Experiment No 1 Aim To study and verify the Truth Tables of AND OR NOT NAND NOR EXOR logic gates Components IC 7400 7402 7404 7408 7432 7486 Apparatus Prototyping board breadboard DC Power Supply Connecting Wires Theory AND AND OR and NOT gates are basic gates XOR and XNOR are universal gates Basically logic gates are electronic circuits because they are made up of number of electronic devices and components Inputs and outputs of logic gates can occur only in two levels These two levels are term HIGH and LOW or TRUE and FALSE or ON AND off OR SIMPLY 1 AND 0 A table which lists all possible combinations of input variables and the corresponding outputs is called a truth table It shows how the logic circuit s output responds to various combinations of logic levels at the inputs AND GATE An AND gate has two or more inputs but only one output The output assumes the logic 1 state only when each one of its inputs is at logic 1 state The output assumes logic 0 state even if one of its input is at logic 0 state AND gate is also called an all or nothing gate The logic symbol truth table of two input AND gate are shown in figure 1 a 1 b respectively The symbol for AND operation is With input variables A B the Boolean expression for output can be written as X A B Logic symbol Truth table Input Output A B X 0 0 0 1 1 0 1 1 0 0 0 1 Fig 1 a Fig 1 b X123X ABAB Pin diagram of IC74LS08 OR GATE Like an AND gate an OR gate may have two or more inputs but only one output The output assumes the logic 1 state even if one of its inputs is in logic 1 state Its output assumes logic 0 state only when each one of its inputs is in logic 0 state OR gate is also called an any or all gate It can also be called an inclusive OR gate because it includes the condition both the input can be present The logic symbol truth table of two input OR gate are shown in figure 1 c 1 d respectively The symbol for OR operation is With input variables A B the Boolean expression for output can be written as X A B Logic symbol Truth table Input Output A B X 0 0 0 1 1 0 1 1 0 1 1 1 Fig 1 c Fig 1 d Pin diagram of IC74LS32 123AX A BXB NOT GATE A NOT gate is also known an inverter has only one input and only one output It is a device whose output is always the complement of its input That is the output of a not gate assumes the logic 1 state when its input is in logic 0 state and assumes the logic 0 state when its input is in logic 1 state The logic symbol truth table of NOT gate are shown in figure 1 e 1 f respectively The symbol for NOT operation is bar With input variable A the Boolean expression for output can be written as This is read as X is equal to a bar Logic symbol Truth table Input Output A 0 1 X 1 0 Fig 1 e Fig 1 f Pin diagram for IC74LS04 NAND GATE NAND gate is universal gate It can perform all the basic logic function NAND means NOT AND that is AND output is NOTed so NAND gate is combination of an AND gate and a NOT gate The output is logic 0 level only when each of its inputs assumes a logic 1 level For any other combination of inputs the output is logic 1 level NAND gate is equivalent to a bubbled OR gate The logic symbol truth table of two input NAND gate are shown in figure 1 g 1 h respectively With input variables A B the Boolean expression for output can be written as Logic symbol Truth table Input Output A B X 0 0 0 1 1 0 1 1 1 1 1 0 Fig 1 g Fig 1 h BA123X ABX Pin diagram for IC74LS00 NOR GATE NOR gate is universal gate It can perform all the basic logic function NOR means NOT OR that is OR output is NOTed so NOR gate is combination of an OR gate and a NOT gate The output is logic 1 level only when each of its inputs assumes a logic 0 level For any other combination of inputs the output is logic 0 level NOR gate is equivalent to a bubbled AND gate The logic symbol truth table of two inputs NOR gate are shown in figure 1 i 1 j respectively With input variables A B the Boolean expression for output can be written as Logic symbol Truth table Input Output A B X 0 0 0 1 1 0 1 1 1 0 0 0 Fig 1 i Fig 1 j BA231XX A B Pin diagram for IC74LS02 EXCLUSIVE OR X OR GATE An X OR gate is a two input one output logic circuit whose output assumes a logic 1 state when one and only one of its two inputs assumes a logic 1 state Under the condition when both the inputs are same either 0 or 1 the output assumes a logic 0 state Since an X OR gate produces an output 1 only when the inputs are not equal it is called as an anti coincidence gate or inequality detector The output of an X OR gate is the modulo sum of its two inputs The logic symbol truth table of two input X OR gate are shown in figure 1 k 1 l respectively The symbol for X OR operation is With input variables A B the Boolean expression for output can be written as X A Logic symbol Truth table X A Input Output A B X 0 0 0 0 1 1 0 1 1 1 1 0 Fig 1 k Fig 1 l BA123X Pin diagram for IC74LS86 Procedure Set up the breadboard Test all required ICs Give various combinations of inputs and check the output Repeat the procedure for each IC LED OFF Green Light Logic 0 Input variables A B Observation Table LED ON RED light Logic 1 Output variable Y Sr No Input A LED Input B LED Output AND Y AB Output OR Y A B Output OR Y A Output XOR Y A B Output NAND Y AB Output NOR Y A B 1 2 3 4 Results and Analysis NOT Gate When logic 1 is applied to one of NOT gate of 7404 IC then output becomes zero When input LED is ON RED the output LED become OFF Green vice versa OR Gate The output of an OR gate is a 1 if one or the other or both of the inputs are 1 but a 0 if both inputs are 0 When One or the other or Both of the input LEDS are ON RED Light …

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