Alciatore D.G., Histand M.B. Introduction to Mechatronics and Measurement Systems

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Questions and Exercises 251

Section 6.5 Boolean Algebra

6.11. Find the result of each of the following expressions:

a . 1 · 0  1 · (0  1)  0 · (1  0)

b . A · B  A · ( A  B)

6.12. Determine a simplified Boolean expression for X in the combinational logic circuit

that follows. Also, complete the timing diagram.

6.13. Prove Equation 6.20 using the basic Boolean algebra laws.

6.14. Prove Equation 6.21 using the basic Boolean algebra laws.

6.15. Verify that Equation 6.22 is correct using a truth table.

6.16. Prove Equation 6.23 using a truth table.

6.17. Prove that the following Boolean identity is correct:

AB  AC  BC  AB  BC

6.18. Prove whether the following Boolean equations are valid or not:

a . ( A · B)  (B · C)  (B · C)  ( A · B)  C

b . A · B · C  A  B  C

c . ( A · B)  (B · C)  (B · C)  ( A · B)  C

6.19. Use a truth table to prove the validity of De Morgan’s laws ( Equations 6.25 and 6.26 )

for two signals (A and B).

6.20. The following circuit is called a multiplexer. Construct a truth table and write out a

Boolean expression for X. Also, explain why the circuit is termed a multiplexer.

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252 CHAPTER 6 Digital Circuits

6.21. For the security system simplified Boolean expression derived in Section 6.6.3 ,

if the input state CD  11 resulted from a malfunction, explain how the alarm

system would respond in different situations?

Section 6.6 Design of Logic Networks

6.22. Create an all-AND and an all-OR representations for the simplified Boolean expres-

sion in Example 6.3. Given that AND and OR gates are available on ICs in groups

of four per IC and inverters are available on ICs in groups of six per IC, how many

ICs would be required to implement the original and each of the two alternative

representations?

6.23. Create an all-OR realization for Equation 6.30 and draw the resulting circuit.

6.24. Design and draw a logic circuit that will drive segment c of a seven-segment LED

display given the 4-bit BCD input DCBA representing decimal numbers from 0 to 9.

Note that the logic circuit will be used in the driver circuit that follows.

driver circuit

logic

circuit

330

segment c

LED

5 V

7-segment

display

6.25. Draw a logic circuit for the following Boolean expression using NAND gates and

inverters only:

X  A · B · C  (A  B) · C

The NAND gates may only have two inputs each.

6.26. Determine a simplified Boolean expression for the following circuit and draw an

equivalent circuit using NOR gates and inverters only:

The NOR gates may only have two inputs each.

6.27. Design a logic circuit for a simple automobile door and seat belt buzzer system.

Assume that sensors are available to provide digital signals representing the door

and seat belt states. Signal A is from the door, where high implies the door is closed;

signal B is from the seat belt, where high implies the seat belt is fastened; and sig-

nal C indicates whether the ignition switch is turned on. Your circuit should output

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Questions and Exercises 253

a signal X that can be used to turn a buzzer on or off, where high implies on. The

buzzer should be on if the ignition is on and if the door is open or the seat belt is not

fastened. Draw your logic circuit and construct a complete truth table.

Section 6.7 Finding a Boolean Expression Given

a Truth Table

6.28. Derive the simplified Boolean expression for X in Question 6.20 using the sum-of-

products method.

6.29. Verify the four expressions for S and C (two each) from Example 6.4 by testing each

with a truth table.

6.30. Document a complete and thorough answer to Class Discussion Item 6.4 .

6.31. Design and draw a full-adder circuit that has two sum bits A

and B

and a lower-

order carry bit C

i - 1

as inputs (see Example 6.4 ). Include a complete truth table and

include sum-of-products Boolean expressions for the output sum bit S

and carry

bit C

Section 6.9 Flip-Flops

6.32. Answer CDI 6.5, demonstrating the results of every row in Table 6.8.

6.33. Construct a complete truth table for a negative edge-triggered T flip-flop including

preset and clear inputs.

6.34. Construct a complete truth table and timing diagram for a negative edge-triggered

D flip-flop including preset and clear inputs.

6.35. Complete the timing diagram for the following circuit.

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254 CHAPTER 6 Digital Circuits

6.36. Complete the timing diagram (see below) for the following circuit.

preset

clear

preset

clear

6.37. Complete the timing diagram (see below) for the following circuit.

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Questions and Exercises 255

Section 6.10 Applications of Flip-Flops

6.38. Document a complete and thorough answer to Class Discussion Item 6.7 .

6.39. Design a circuit that will store data from four binary sensors (presenting either a high

or low value) when an enable pulse from a digital source first goes high. Assume that

the enable input is normally low and the pulse is high for 1 sec.

6.40. Draw a timing diagram for all of the signals in Figure 6.20 , showing all steps in the

transmission of the nibble (4-bit string) 1011, starting with the MSB first.

6.41. Draw a timing diagram for all of the signals in Figure 6.21 , showing all steps in the

transmission of the nibble (4-bit string) 1011, starting with the MSB first.

6.42. Using JK flip-flops, design a circuit that will produce a clock signal of half the

frequency of an input clock signal. If the input clock signal is asymmetric, will

the output clock also be asymmetric?

6.43. You have a digital sensor such as a photo-interrupter that is normally low, but when

activated will go high for a short but unspecified period of time. Design a circuit that

will capture the output from the sensor and hold it until you apply a reset signal.

6.44. Design a sequential logic circuit to store the state of an SPDT switch when a bounce-

free NO button (see Section 9.2.1 for details) is first pressed down and increment a

counter when the button is released if the switch was down when the button was first

pressed. Assume the bounce-free button and counter are purchased off the shelf and

need not be designed. Draw a complete circuit diagram of your solution and show a

timing diagram, assuming the SPDT switch exhibits switch bounce.

Section 6.11 TTL and CMOS Integrated Circuits

6.45. Document a complete and thorough answer to Class Discussion Item 6.12 .

6.46. You are constrained in a digital design to interface a 74LS00 NAND gate to a 4011B

NAND gate. Draw the schematic of a circuit necessary to do this properly.

6.47. Why can you not have large TTL fan-out from the output of a CMOS device?

Section 6.12 Special Purpose Digital Integrated

Circuits

6.48. Derive a Boolean expression for the output columns c and e of Table 6.11 using

either the product-of-sums or sum-of-products techniques presented in Section 6.7.

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256 CHAPTER 6 Digital Circuits

6.49. Using the information in a TTL data book, draw a complete schematic for a 7490

decade counter with BCD output. Include a reset feature using the four R lines in the

timing diagram that follows. Also, complete the timing diagram.

7490

CKB

R0(1)

R0(2)

R9(1)

R9(2)

CKA

GND

R0(1)

R0(2)

R9(1)

R9(2)

CKA

CKB

6.50. How does the decade counter differ from the 4-bit binary counter presented in

Figure 6.19 ?

6.51. Given a Schmitt trigger operating between 0 and 5 V, assume that the lower threshold

is 1 V and the upper threshold is 4 V. Given the following input signals applied to the

Schmitt trigger, sketch the corresponding output from the Schmitt trigger for one

cycle of each signal:

a. 2.5  1.0 sin (2  t ) V

b. 2.5  2.0 sin (2  t ) V

c. 1.5  1.5 sin (2  t ) V

d. 3.0  1.5 sin (2  t ) V

6.52. Determine the exact pulse width as a function of the resistance and capacitance in a

one-shot circuit (see Equation 6.36 ).

6.53. Design and draw the schematic for a 555 oscillator that generates a 1-Hz clock

signal.

6.54. Show all of the detailed algebraic steps necessary to derive Equation 6.42.

6.55. Document a complete and thorough answer to Class Discussion Item 6.14 .

Section 6.13 Integrated Circuit System Design

6.56. Document a complete and thorough answer to Class Discussion Item 6.16 .

6.57. Look up the 74LS90 decade counter in a digital handbook. Using the information

found there, design a circuit that will turn on an LED after 100 occurrences of a

digital event. The design should be a schematic. Include details of input codes to

the IC necessary for decade counting.

6.58. For the circuit you designed in Question 6.44 , or for a design provided by your

instructor, verify whether or not switch bounce (from the SPDT switch) has an effect.

Also, would the circuit still work if the NO button were not bounce-free? If not, how

could the design be modified to deal with this?

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Bibliography 257

6.59. You are provided with a coin slot through which people push coins. The bottom of

the coin always slides along the bottom of the slot. People feed dimes, nickels, and

quarters into the slot. Photo sensors are available and can be placed at any height to

detect when portions of coins pass through the slot. The output of a sensor is high

when its beam is interrupted; otherwise, it is low. Design a system that will light a

red LED when a dime passes through, a yellow LED when a nickel passes through,

and a green LED when a quarter passes through.

6.60. Assuming you have been successful in Question 6.59 , extend the design to also count

the number of dimes, nickels, and quarters passing through the slot.

BIBLIOGRAPHY

Horowitz , P. and Hill , W. , The Art of Electronics, 2nd Edition, Cambridge University Press,

New York , 1989 .

Mano , M. , Digital Logic and Computer Design, Prentice-Hall, Englewood Cliffs , NJ, 1979 .

McWhorter , G. and Evans , A. , Basic Electronics, Master Publishing, Richardson , TX, 1994 .

Mims , F. , Getting Started in Electronics, Radio Shack Archer Catalog No. 276-5003A, 1991 .

Mims , F. , Engineers Mini-Notebook: 555 Circuits, Radio Shack Archer Catalog No. 276-

5010, 1984 .

Mims , F. , Engineer’s Mini-Notebook: Digital Logic Circuits, Radio Shack Archer Catalog

No. 276-5014, 1986 .

Stiffler , A. , Design with Microprocessors for Mechanical Engineers, McGraw-Hill,

New York , 1992 .

Texas Instruments, TTL Logic Data Book, Dallas, TX, 1988 .

Texas Instruments, Operational Amplifiers and Comparators, Volume B, Dallas, TX, 1995 .

Texas Instruments, TTL Linear Circuits Data Book, Volume 3, Dallas, TX, 1992 .

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258

Microcontroller

Programming and

Interfacing

his chapter describes how to program and interface a microcontroller. Various

input and output devices are also presented.■

INPUT SIGNAL

CONDITIONING

AND INTERFACING

- discrete circuits

- amplifiers

- filters

- A/D,

D/D

OUTPUT SIGNAL

CONDITIONING

AND INTERFACING

- D/A, D/D

- PWM

power transistors

power op amps

GRAPHICAL

DISPLAYS

- LEDs

digital displays

LCD

- CRT

SENSORS

switches

- potentiometer

- photoelectrics

- digital encoder

- strain gage

- thermocouple

- accelerometer

- MEMs

ACTUATORS

- solenoids, voice coils

- DC motors

- stepper motors

- servo motors

- hydraulics, pneumatics

MECHANICAL SYSTEM

- system model - dynamic response

DIGITAL CONTROL

ARCHITECTURES

- logic circuits

microcontroller

- SBC

- PLC

sequencing and timing

logic and arithmetic

control algorithms

communication

- amplifiers

CHAPTER OBJECTIVES

After you read, discuss, study, and apply ideas in this chapter, you will:

1. Understand the differences among microprocessors, microcomputers, and

microcontrollers

2. Know the terminology associated with a microcomputer and microcontroller

3. Understand the architecture and principles of operation of a microcontroller

CHAPTER

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7.1 Microprocessors and Microcomputers 259

4. Understand the basic concepts of assembly language programming

5. Understand the basics of higher level programming languages such as

PicBasic Pro

6. Be able to write programs to control PIC microcontrollers

7. Be able to interface microcontrollers to input and output devices

8. Be able to design microcontroller-based mechatronic systems

9. Be aware of several practical considerations that will help you prototype,

program, and debug microcontroller-based systems

10. Be able to select an appropriate source of power for a microcontroller-based

system

7.1 MICROPROCESSORS AND

MICROCOMPUTERS

The digital circuits presented in Chapter 6 allow the implementation of combina-

tional and sequential logic operations by interconnecting ICs containing gates and

flip-flops. This is considered a hardware solution because it consists of a selection

of specific ICs, which when hardwired on a circuit board, carry out predefined func-

tions. To make a change in functionality, the hardware circuitry must be modified

and may require a redesign. This is a satisfactory approach for simple design tasks

(e.g., the security system presented in Section 6.6 and the digital tachometer pre-

sented in Design Example 6.1). However, in many mechatronic systems, the control

tasks may involve complex relationships among many inputs and outputs, making

a strictly hardware solution impractical. A more satisfactory approach in complex

digital design involves the use of a microprocessor-based system to implement a

software solution. Software is a procedural program consisting of a set of instruc-

tions to execute logic and arithmetic functions and to access input signals and con-

trol output signals. An advantage of a software solution is that, without making

changes in hardware, the program can be easily modified to alter a mechatronic

system’s functionality.

A microprocessor is a single, very-large-scale-integration (VLSI) chip that con-

tains many digital circuits that perform arithmetic, logic, communication, and control

functions. When a microprocessor is packaged on a printed circuit board with other

components, such as interface and memory chips, the resulting assembly is referred

to as a microcomputer or single-board computer. The overall architecture of a

typical microcomputer system using a microprocessor is illustrated in Figure 7.1 .

The microprocessor, also called the central processing unit (CPU) or micro-

processor unit (MPU), is where the primary computation and system control

operations occur. The arithmetic logic unit (ALU) within the CPU executes math-

ematical functions on data structured as binary words. A word is an ordered set of

bits, usually 8, 16, 32, or 64 bits long. The instruction decoder interprets instructions

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Figure 7.1 Microcomputer architecture.

data lines

address lines

control lines

data

registers

ALU

instruction

decoder

instruction

microprocessor

memory (RAM, ROM, EPROM)

external I/O (A/D, D/A, D/D)

mass memory (disk, tape, CD-ROM)

system I/O (keyboard, printer,

monitor, modem, network devices)

computer

peripherals

switches,

sensors, and actuators

external

mechatronic

system hardware

microcomputer

bus

control

unit

260 CHAPTER 7 Microcontroller Programming and Interfacing

fetched sequentially from memory by the control unit and stored in the instruction

bit manipulation, such as binary addition and logic functions, on words stored in the

CPU data registers. The ALU results are also stored in data registers and then trans-

ferred to memory by the control unit.

The bus is a set of shared communication lines that serves as the central nervous

system of the computer. Data, address, and control signals are shared by all system

components via the bus. Each component connected to the bus communicates infor-

mation to and from the bus via its own bus controller. The data lines, address lines,

and control lines allow a specific component to access data addressed to that compo-

nent. The data lines are used to communicate words to and from data registers in the

various system components such as memory, CPU, and input/output (I/O) peripher-

als. The address lines are used to select devices on the bus or specific data locations

within memory. Devices usually have a combinational logic address decoder circuit

that identifies the address code and activates the device. The control lines transmit

read and write signals, the system clock signal, and other control signals such as

system interrupts, which are described in subsequent sections.

A key to a CPU’s operation is the storage and retrieval of data from a memory

device. Different types of memory include read-only memory (ROM), random-

access memory (RAM), and erasable-programmable ROM (EPROM). ROM is

used for permanent storage of data that the CPU can read, but the CPU cannot write

data to ROM. ROM does not require a power supply to retain its data and therefore

is called nonvolatile memory. RAM can be read from or written to at any time, pro-

vided power is maintained. The data in RAM is considered volatile because it is lost

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