are the symbols associated with the logic gates. TheFigure 4-8.—Example of pulse-repetition time (PRT).Pulse-repetition frequency (PRF) —The PRF ofa signal is the number times per second that a completecycle of the signal occurs and is expressed in hertz (Hz).Learn the relationships between PW, PRT, and PRF.They can be very helpful and can save you valuable timewhen you analyze waveshapes. You can apply them tonon-symmetrical and symmetrical waveshapes. Thebasic formula is as follows: PRF = 1/PRT.Using figure 4-8, we can calculate the PRF. Sincethe PRT is 30 msec, then using the formula would give:PRF = 1/PRT= 1/30 msec = 33 kHz.DIGITAL IC GROUPSThe basic building blocks of digital logic circuitscontained in a computer are logic gates. The logiccircuits contained in digital logic circuits can beclassified into two groups: combinational andsequential.Combinationaldigitallogiccircuits—The basicbuilding block for combinational digital circuits is thelogic gate.Sequentialdigitallogiccircuits—The basicbuilding block for sequential digital circuits is theflip-flop. Flip-flops are formed from variations of thecombinational digital circuits.Digital Logic GatesDigital logic gates are the basis for operations in adigital computer.The digital logic gates you willencounter operate with binary numbers; hence, the termdigital logic gates. They are combinational andsequential logic elements.The AND, OR, and NOT logic gates are the basisfor all logic gates. These three logic gates are used indifferent combinations and variations to form logicgates that perform decision-making functionsthroughout the computer. Included in our discussionbasic logic gates with their symbols are as follows:Simple variations of the three basic functions AND,OR, and NOT gates are used as building blocks for theother types of logic gates used in the computer. Theselogic gates with their symbols are as follows:4-9

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