1. Principles & Applications
Digital Electronics
Principles & Applications
Seventh Edition
Roger L. Tokheim
Chapter 3
Logic Gates
©2008 The McGraw-Hill Companies, Inc. All rights reserved.

2. INTRODUCTION The AND Gate Gates with More Than Two Inputs The OR Gate
The Inverter
The NAND Gate
The NOR Gate
The XOR Gate
The XNOR Gate
NAND as Universal Gate
Gates with More Than Two Inputs
Using Inverters to Convert Gates
TTL & CMOS Gates
Troubleshooting Gating Circuits
IEEE Logic Symbols
Logic Functions using Software

3. “All or Nothing Gate”
Boolean Expression: A · B = Y
Truth Table (See next slide)
The AND Gate

4. Truth Table - AND Gate

5. What is the output of the AND gate?
QUIZ
What is the output of the AND gate? L ? H ?
Low
High L H ? ? H L
Low
Low
Unique Output: Output HIGH only when all inputs are HIGH.

6. The OR Gate “Any or All Gate” Boolean Expression: A + B = Y
Truth Table (See next slide)
The OR Gate

7. Truth Table - OR Gate

8. What is the output of the OR gate?
QUIZ
What is the output of the OR gate? ? ? H H L
High
High ? ? L L H
Low
High
Unique Output: Output LOW only when all inputs are LOW.

9. The Inverter NOT Circuit
Gives output that is not the same as the input.
Boolean Expression: Y = A or Y = A‘
Double inverting: A = A
NOT gate inverts, or complements, or negates
The Inverter

10. QUIZ
If the input to an inverter is LOW, the output will be __________.
HIGH
2. If the input to an inverter is HIGH, the output will be __________.
LOW
3. A NOT gate is said to invert, to negate or to complement the input. (True or False)
True
4. A NOT gate is also called commonly called a(n) __________ (AND gate, inverter).
inverter

11. The NAND Gate NOT AND or inverted AND function.
Boolean Expression: A · B = Y
or (A · B)' = Y
Truth Table (See next slide)
The NAND Gate

12. Truth Table - NAND Gate

13. What is the output of the NAND gate?
QUIZ
What is the output of the NAND gate? ? ? L L H
High
High ? ? H L H
Low
High
Unique Output: Output LOW only when all inputs are HIGH.

14. NOT OR or Inverted OR
Boolean Expression: A + B = Y
or (A + B)' = Y
Truth Table (See next slide)
The NOR Gate

15. Truth Table - NOR Gate

16. QUIZ What is the output of the NOR gate? ? ? ? ? L L H High Low H L H
Unique Output: Output HIGH when all inputs are LOW.

17. Known as “Exclusive OR” Gate
“Anything but not all” Gate
Boolean Expression: A  B = Y
Truth Table (See next slide)
The XOR Gate

18. Truth Table - XOR Gate

19. What is the output from the XOR gate?
QUIZ
What is the output from the XOR gate? L ? ? L H ?
Low
High ? H ? H L
High ?
Low
XOR output is HIGH only when odd number of inputs are HIGH

20. The XNOR Gate Known as the Exclusive NOR Gate The Inverted XOR
Boolean Expression: A  B = Y
or (A  B)' = Y
Truth Table (See next slide)
The XNOR Gate

21. Truth Table - XNOR Gate

22. QUIZ What is the output from this XNOR gate? ? ? ? High Low High Low ?
XNOR output is HIGH only when odd number of inputs are LOW

23. The NAND as a Universal Gate
“Universal gate” can be used in combination to create any other logic function.
Example:
Shorting NAND inputs Yields the NOT logic function
Equal to the
OR logic function
A + B

24. QUIZ
1. NAND gates can be wired together to convert to other logic functions (True or False).
True
2. These two NAND gates wired together will produce the ______ (AND, XOR) logic function.
AND

25. Using Inverters to Convert Gates
For example:

26. QUIZ
1. This combination of gates will generate the ______ (NAND, OR) logic function.
NAND
2. This combination of gates will generate the ______ (AND, OR) logic function.
AND

27. Practical Logic Gates ICs - Integrated Circuit Form TTL Family of ICs
CMOS Family of ICs
TTL = Transistor-Transistor Logic
CMOS = Complementary Metal Oxide Semiconductor

28. transistor-transistor logic
QUIZ
1. Practical logic gates (AND-, OR-, NAND-, NOT-gates) are packaged in __________ form. IC
2. Two popular families of ICs used to manufacture logic gate ICs are __________.
TTL and CMOS
3. In digital electronics, TTL commonly refers to a family of ICs. TTL stands for __________.
transistor-transistor logic
4. In digital electronics, logic gates are manufactured using either TTL or __________ technology.
CMOS

29. Troubleshooting Simple Gate Circuits
Logic probe - equipment used to test circuits
Feel top of IC to determine if it is hot
Look for broken connections, signs of excessive heat
Smell for overheating
Check power source
Trace path of logic through circuit

30. QUIZ
1. A simple hand-held instrument called a __________ (logic probe, oscilloscope) can be used for troubleshooting simple logic gate circuits.
logic probe
2. The first three steps in troubleshooting are to use your senses to (1) feel the top of the ICs for overheating, (2) look for broken connections, and (3) __________ for signs of overheating.
smell
3. The fourth step in troubleshooting is to use a logic probe to check the power sources. (True or False)
True

31. 1 IEEE Logic Symbols A different set of symbols without unique shapes.
Not very popular at this time.
Examples:
& A B Y
AND gate A B Y 1
OR gate

32. Programming Logic Functions using the BASIC Stamp® Module
One trend in electronics is the development of programmable ICs.
A second trend in electronics is the use a billions of inexpensive embedded devices called microcontrollers.
A popular microcontroller used extensively by schools is the BASIC Stamp® module by Parallax, Inc.
BASIC Stamp® modules are programmed using a student-friendly version of B.A.S.I.C.
Programming of the BASIC Stamp® is done on a PC. The program is downloaded into the BASIC Stamp®. The downloaded programmed is then held in the BASIC Stamp® module’s memory. The program starts at the beginning each time power to the module is turned on.

33. QUIZ microcontroller PC True
The BASIC Stamp® module contains a programmable device called a _____.
microcontroller
2. Programming for the BASIC Stamp® is done on a _____ (cell phone, PC) and then downloaded into the module’s memory. PC
3. A microcontroller is an inexpensive programmable device that is commonly embedded in everyday appliances, etc. (True or False)
True

34. Using the BASIC Stamp® Module
Step 1: Program the BS2 module using in PBASIC language. The key line of code is: Y = A & B which represents AB=Y or input A ANDed with input B.
Digital Inputs
Input A = HIGH
Input B = HIGH
Step3: Disconnect PC.
Input A = LOW
Input B = LOW A
Input A = HIGH
Input B = LOW B
Step 4: Turn power OFF and then ON. The program will start at the beginning. Observe the outputs with different inputs.
Step 2: Download the PBASIC program from the PC to the BASIC Stamp® 2 module.
Digital Output
HIGH
LOW
LOW Y

35. PBASIC Code for Logic Functions
Logic Function PBASIC code for BS2
AND Y = A & B
OR Y = A | B
NOT Y = ~A
NAND Y = ~(A & B)
NOR Y = ~(A | B)
XOR Y = A ^ B
XNOR Y = ~(A ^ B)

36. QUIZ Y = A | B Y = ~(A & B) Y = A ^ B
1. What is the PBASIC code used when programming
the BASIC Stamp® module for the 2-input OR logic
function?
Y = A | B
2. What is the PBASIC code used when programming
the BASIC Stamp® module for the 2-input NAND logic
function?
Y = ~(A & B)
3. What is the PBASIC code used when programming
the BASIC Stamp® module for the 2-input XOR logic
function?
Y = A ^ B

37. REVIEW The AND Gate Gates with More Than Two Inputs The OR Gate
The Inverter
The NAND Gate
The NOR Gate
The XOR Gate
The XNOR Gate
NAND as Universal Gate
Gates with More Than Two Inputs
Using Inverters to Convert Gates
TTL & CMOS Gates
Troubleshooting Gating Circuits
IEEE Logic Symbols
Logic Functions using Software