ES210L, Digital Circuits and Logic Design Lab

Reporter Name: / Date:
Partner Names / Group No.:

Lab 1:Combinations of Logical Gates*

  1. Objectives
  1. Review the logic gates that are widely used in electronic systems
  2. Review the operation of some common logic gates.
  1. Introduction

A logic gate is a device that performs a logical operation on one or more logical inputs, and produces a single logical output.Logic gates are used in most electronic systems including computers, control, communications, etc. Basic logic gates include AND, OR, NOT, NAND, NOR. Figure 1 shows the common logic gates with 7400 series TTL technology.

  1. Explain briefly under each gate what it is.

  1. Which gate is most commonly used?


What is a NOT gate? /
What is an OR gate?

What is an AND gate? /
What is a NAND gate?

What is a NOR gate? / Note:74LS – Low-power Schottky(most popular) uses Schottky diode clamps for protection.

Figure 1. View of the some common logic packages and the pin voltages

  1. Parts needed

  • A Digital Multimeter
  • A +5 V power supply
  • A breadboard/protoboard and Wires
/
  • A 74LS04 (NOT gate)
  • A 74LS00 (NAND gate)
  • Datasheets of the gates from the Internet

  1. Procedure

For your report, you can save a copy of this instruction sheet with file name “YourLastName_LogicGates_Lab1.docx” & fill in the answers to the questions for submission.

  1. Use the datasheet of TTL gate 74LS04by Texas Instrumentsand answer the following questions in the 2ndcolumn.

What does TTL mean and what does it use?
What does “LS” in 74LSxx family mean regarding the power dissipation, switching speed?
What is the function of the 74LS04 gate?
How many gates NOT are there in each package?
What is the absolute maximum voltage that can be applied to inputs?
What is the nominal supply voltage of 7404?
What should be the DC voltage at pin #14 of 7404?
What should be the DC voltage at pin #7 of 7404?
What is the minimum input voltage of Logical “1”= High logic?
What is the maximum input voltage of Logical “0”= Low logic?
If input voltage is between the minimum and maximum values above (e.g, 1.5V, would you interpret it as High or Low logic?
How many transistors do you identify in Texas Instrument 74LS04?
How many diodes (Schottky diodes) do you identify in 74LS04?
  1. Setup the circuit as shown in Fig. 2 using 74LS04 Hex Inverter. An Inverter (or NOT)gate inverts the input signal. Using the switch and the LEDs verifythe inverter function and report your observations in the table below. You can use the LEDs on the protoboard in which case you DO NOT need to use the 330-Ohm resistors and can connect the outputs of 74LS04 to the LEDs directly.

/ Fig. 2. Three NOT gates in series.
Switch at / U1A output Voltage / LED1 (on/off) / U1B output voltage / LED2 (on/off) / U1C output voltage / LED3 (on/off) 18%
+5 V
0 V
Is it what you expect?
  1. What are the threshold voltages at which a NOT gate output switches from Logical “1” = High logicto Logical “0” =Low logic and vice versa?

Use Fig. 2 and connect the input of Inverter U1A to a voltage between 0 to 5 Vusing Agilent Power Supply (0 to +6Vbut limit it to +5V) or another source together with a Digital Voltmeter to measure the input voltage. Now starting from 0V (note that U1A output is at Logical “1”), increase the voltage at the input and watch when the output at U1Amakes a big change and switches from High logic to Low logic. Call this input voltage V0H and record it in the table below. Next starting from voltage around 4.5 V at the input (note that U1A output is at Logical “0”), decrease the voltage and watch the output voltage as soon as it switches from Low logic to High logic. Call this input voltage V1L and record it in the table below. Compare these voltageswith 74LS04 data sheet and conclude.

Threshold Voltage (V) / V0H = input from low to high / V1L = input from high to low
U1A Inverter gate
  1. Setup the circuit as shown in Fig. 3 using 74LS00 Quad NAND gates.

/ Fig 3. Two “NAND” gates with three inputs A, B, and C

Express and simplify the output at U1B as a function of A, B, and C inputs. You can use De Morgan’s Law.

U1B output =
  1. Assume a logical variable (A, B, or C) is at “logical 1” when the corresponding switch (S1, S2, or S3) is connected to +5 V. For eachS1-S2-S3 combination record the status of the corresponding LED at U1B output.How would this output compare with theoutput of 3-input NAND= (A.B.C)’. You can use DeMorgan’s Law for your proof.

A = S1 / B = S2 / C = S3 / Output LED (High/Low) / (A.B.C)’ / Is (ABC)’ = U1B outputs?
Why?
0 / 0 / 0
0 / 0 / 1
0 / 1 / 0
0 / 1 / 1
1 / 0 / 0
1 / 0 / 1
1 / 1 / 0
1 / 1 / 1
  1. Feedback/Comments (your comments will help improving this labgain points)4 %

Was the instruction clear enough? Anyerror?
How difficult was the experiment for you?
Do you have any observations to make?
  1. Report
  2. In your report, keep the title of the experiment, your & your partners’ names, and your group number. Include your measurements and answers you obtained in the tables above. Do not include the unnecessary parts such as the objectives, instructions, and procedures.
  3. Submit your report to the instructor at the end of the session.

Dr. Ali Kujoory10/2/20181