Introduction to Embedded Systems: Using ANSI C and the Arduino Development Environment

276 Pages·2010·1.67 MB·English

by  David Russell, Mitchell Thornton

~
\ i \) I\ l;-\ '\ & ~ ·1 :\ Y I' l H) I I'll I\ I I\ II I I\\

Introduction to
Embedded Systems

Using ANSI C and the
Arduino Development Environment

David Russell

Introduction to
Embedded Systems

Using ANSI C and
the Arduino Development Environment

Copyright © 2010 by Morgan & Claypool

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in
any form or by any means—electronic, mechanical, photocopy, recording, or any other except for brief quotations in
printed reviews, without the prior permission of the publisher.

Introduction to Embedded Systems: Using ANSI C and the Arduino Development Environment

David J. Russell

www.morganclaypool.com

ISBN: 9781608454983
paperback
ISBN: 9781608454990
ebook

DOI 10.2200/S00291ED1V01Y201007DCS030

A Publication in the Morgan & Claypool Publishers series
SYNTHESIS LECTURES ON DIGITAL CIRCUITS AND SYSTEMS

Lecture #30
Series Editor: Mitchell A. Thornton, Southern Methodist University
Series ISSN
Synthesis Lectures on Digital Circuits and Systems
Print 1932-3166
Electronic 1932-3174

Synthesis Lectures on Digital
Circuits and Systems

Editor
Mitchell A.Thornton, Southern Methodist University

The Synthesis Lectures on Digital Circuits and Systems series is comprised of 50- to 100-page books
targeted for audience members with a wide-ranging background. The Lectures include topics that are
of interest to students, professionals, and researchers in the area of design and analysis of digital circuits
and systems. Each Lecture is self-contained and focuses on the background information required to
understand the subject matter and practical case studies that illustrate applications. The format of a
Lecture is structured such that each will be devoted to a specific topic in digital circuits and systems
rather than a larger overview of several topics such as that found in a comprehensive handbook. The
Lectures cover both well-established areas as well as newly developed or emerging material in digital
circuits and systems design and analysis.

Introduction to Embedded Systems: Using ANSI C and the Arduino Development
Environment
David J. Russell
2010

Arduino Microcontroller: Processing for Everyone! Part II
Steven F. Barrett
2010

Arduino Microcontroller Processing for Everyone! Part I
Steven F. Barrett
2010

Digital System Verification: A Combined Formal Methods and Simulation Framework
Lun Li and Mitchell A. Thornton
2010

Progress in Applications of Boolean Functions
Tsutomu Sasao and Jon T. Butler
2009

Embedded Systems Design with the Atmel AVR Microcontroller: Part II
Steven F. Barrett
2009

iv

Embedded Systems Design with the Atmel AVR Microcontroller: Part I
Steven F. Barrett
2009

Embedded Systems Interfacing for Engineers using the Freescale HCS08 Microcontroller II:
Digital and Analog Hardware Interfacing
Douglas H. Summerville
2009

Designing Asynchronous Circuits using NULL Convention Logic (NCL)
Scott C. Smith and Jia Di
2009

Embedded Systems Interfacing for Engineers using the Freescale HCS08 Microcontroller I:
Assembly Language Programming
Douglas H.Summerville
2009

Developing Embedded Software using DaVinci & OMAP Technology
B.I. (Raj) Pawate
2009

Mismatch and Noise in Modern IC Processes
Andrew Marshall
2009

Asynchronous Sequential Machine Design and Analysis: A Comprehensive Development of
the Design and Analysis of Clock-Independent State Machines and Systems
Richard F. Tinder
2009

An Introduction to Logic Circuit Testing
Parag K. Lala
2008

Pragmatic Power
William J. Eccles
2008

Multiple Valued Logic: Concepts and Representations
D. Michael Miller and Mitchell A. Thornton
2007

Finite State Machine Datapath Design, Optimization, and Implementation
Justin Davis and Robert Reese
2007

v

Atmel AVR Microcontroller Primer: Programming and Interfacing
Steven F. Barrett and Daniel J. Pack
2007

Pragmatic Logic
William J. Eccles
2007

PSpice for Filters and Transmission Lines
Paul Tobin
2007

PSpice for Digital Signal Processing
Paul Tobin
2007

PSpice for Analog Communications Engineering
Paul Tobin
2007

PSpice for Digital Communications Engineering
Paul Tobin
2007

PSpice for Circuit Theory and Electronic Devices
Paul Tobin
2007

Pragmatic Circuits: DC and Time Domain
William J. Eccles
2006

Pragmatic Circuits: Frequency Domain
William J. Eccles
2006

Pragmatic Circuits: Signals and Filters
William J. Eccles
2006

High-Speed Digital System Design
Justin Davis
2006

vi

Introduction to Logic Synthesis using Verilog HDL
Robert B.Reese and Mitchell A.Thornton
2006

Microcontrollers Fundamentals for Engineers and Scientists
Steven F. Barrett and Daniel J. Pack
2006

Introduction to
Embedded Systems

Using ANSI C and
the Arduino Development Environment

David J. Russell
University of Nebraska-Lincoln

SYNTHESIS LECTURES ON DIGITAL CIRCUITS AND SYSTEMS #30

C
M
&

cLaypool
Morgan
publishers
&

ABSTRACT

Many electrical and computer engineering projects involve some kind of embedded system in which
a microcontroller sits at the center as the primary source of control.The recently-developed Arduino
development platform includes an inexpensive hardware development board hosting an eight-bit
ATMEL ATmega-family processor and a Java-based software-development environment. These
features allow an embedded systems beginner the ability to focus their attention on learning how to
write embedded software instead of wasting time overcoming the engineering CAD tools learning
curve.
The goal of this text is to introduce fundamental methods for creating embedded software in
general, with a focus on ANSI C. The Arduino development platform provides a great means for
accomplishing this task. As such, this work presents embedded software development using 100%
ANSI C for the Arduino’s ATmega328P processor. We deviate from using the Arduino-specific
Wiring libraries in an attempt to provide the most general embedded methods.In this way,the reader
will acquire essential knowledge necessary for work on future projects involving other processors.
Particular attention is paid to the notorious issue of using C pointers in order to gain direct access
to microprocessor registers, which ultimately allow control over all peripheral interfacing.

KEYWORDS

embedded systems, embedded software, embedded development, microcontroller, mi-
croprocessor, ANSI C, Arduino, ATmega328P

To my best friend Jamie
and our three wonderful kids:
Gates, Gracen, and Gavin

xi

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
1.1
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2
Digital Representation of Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3
Digital Logic Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.4
Digital Vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.5
Information Representation in a Digital Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.5.1
Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.5.2
Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2
ANSI C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.1.1
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.2
Essential Elements of the Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.3
Formatted Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.4
Variables and Arithmetic Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.4.1
Variable Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2.4.2
Type Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.4.3
Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

2.4.4
Arithmetic Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

2.4.5
Relational and Logical Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

2.4.6
Increment and Decrement Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

2.4.7
Bitwise Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

2.4.8
Assignment Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

2.4.9
Conditional Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

2.5
Control Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.5.1
If-Else . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.5.2
Else-If . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.5.3
Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.5.4
Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

xii

2.5.5
Infinite Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

2.5.6
Miscellaneous (Please Don’t Use) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

2.6
Functions and Program Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

2.7
Scope Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

2.8
Pointers and Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2.8.1
Passing by Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

2.8.2
Dynamic Memory Allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

2.9
Multi-dimensional Arrays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

2.10
Function Pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

2.11
Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
2.11.1
Typedef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

2.12
Unions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

2.13
Bit-fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

2.14
Variable-length Argument Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

3
Introduction to Arduino . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.1
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

3.2
Experiments Using the Arduino Duemilanove Development Board . . . . . . . . . . . 80

3.3
Arduino Tools Tutorial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

4
Embedded Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

4.2
Debugging the Arduino Tutorial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

5
ATmega328P Architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

5.2
AVR CPU Core . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

6
General-Purpose Input/Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6.1
Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6.1.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

6.1.2
Basic Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

6.1.3
Pin-muxing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

6.2
Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.2.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

6.2.2
Internal Pull-up Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

xiii

6.3
Accessing GPIO lines in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
6.3.1
Managing Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

6.3.2
Managing Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

6.4
Pertinent Register Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
6.4.1
PORTB - The Port B Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

6.4.2
DDRB - The Port B Data Direction Register . . . . . . . . . . . . . . . . . . . . . 108

6.4.3
PINB - The Port B Input Pins Address. . . . . . . . . . . . . . . . . . . . . . . . . . . 108

6.4.4
PORTC - The Port C Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

6.4.5
DDRC - The Port C Data Direction Register . . . . . . . . . . . . . . . . . . . . . 108

6.4.6
PINC - The Port C Input Pins Address . . . . . . . . . . . . . . . . . . . . . . . . . . 109

6.4.7
PORTD - The Port D Data Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

6.4.8
DDRD - The Port D Data Direction Register . . . . . . . . . . . . . . . . . . . . . 109

6.4.9
PIND - The Port D Input Pins Address . . . . . . . . . . . . . . . . . . . . . . . . . . 109

7
Timer Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
7.1
Pulse Width Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
7.1.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

7.1.2
Demodulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

7.1.3
Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

7.2
Input Capture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

7.3
Pertinent Register Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
7.3.1
TCCR0A - Timer/Counter0 Control Register A . . . . . . . . . . . . . . . . . . 120

7.3.2
TCCR0B - Timer/Counter0 Control Register B . . . . . . . . . . . . . . . . . . . 122

7.3.3
TCNT0 - Timer/Counter0 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

7.3.4
OCR0A - Output Compare0 Register A . . . . . . . . . . . . . . . . . . . . . . . . . 123

7.3.5
OCR0B - Output Compare0 Register B . . . . . . . . . . . . . . . . . . . . . . . . . . 123

7.3.6
TCCR1A - Timer/Counter1 Control Register A . . . . . . . . . . . . . . . . . . 123

7.3.7
TCCR1B - Timer/Counter1 Control Register B . . . . . . . . . . . . . . . . . . . 125

7.3.8
TCCR1C - Timer/Counter1 Control Register C . . . . . . . . . . . . . . . . . . 126

7.3.9
TCNT1H and TCNT1L - Timer/Counter1 Register . . . . . . . . . . . . . . 127

7.3.10
OCR1AH and OCR1AL - Output Compare1 Register A . . . . . . . . . . 127

7.3.11
OCR1BH and OCR1BL - Output Compare1 Register B . . . . . . . . . . . 128

7.3.12
ICR1H and ICR1L - Input Capture1 Register . . . . . . . . . . . . . . . . . . . . 128

7.3.13
TCCR2A - Timer/Counter2 Control Register A . . . . . . . . . . . . . . . . . . 128

7.3.14
TCCR2B - Timer/Counter2 Control Register B . . . . . . . . . . . . . . . . . . . 130

7.3.15
TCNT2 - Timer/Counter2 Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

7.3.16
OCR2A - Output Compare2 Register A . . . . . . . . . . . . . . . . . . . . . . . . . 132

xiv

7.3.17
OCR2B - Output Compare2 Register B . . . . . . . . . . . . . . . . . . . . . . . . . . 132

7.3.18
ASSR - Asynchronous Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

7.3.19
GTCCR - General Timer/Counter Control Register . . . . . . . . . . . . . . . 133

8
Analog Input Ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.1
Analog-to-Digital Converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.1.1
ADC Peripheral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

8.2
Analog Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

8.3
Pertinent Register Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
8.3.1
ADMUX - ADC Multiplexer Selection Register . . . . . . . . . . . . . . . . . . 140

8.3.2
ADCSRA - ADC Control and Status Register A . . . . . . . . . . . . . . . . . . 142

8.3.3
ADCH and ADCL - ADC Data Register . . . . . . . . . . . . . . . . . . . . . . . . 143

8.3.4
ADCSRB - ADC Control and Status Register B . . . . . . . . . . . . . . . . . . 143

8.3.5
DIDR0 - Digital Input Disable Register 0 . . . . . . . . . . . . . . . . . . . . . . . . 144

8.3.6
ACSR - Analog Comparator Control and Status Register . . . . . . . . . . . 144

8.3.7
DIDR1 - Digital Input Disable Register 1 . . . . . . . . . . . . . . . . . . . . . . . . 145

9
Interrupt Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
9.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
9.1.1
Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

9.1.2
ISR and Main Task Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

9.1.3
ATmega328P Interrupts in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

9.2
Pertinent Register Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
9.2.1
EICRA - External Interrupt Control Register A . . . . . . . . . . . . . . . . . . . 154

9.2.2
EIMSK - External Interrupt Mask Register . . . . . . . . . . . . . . . . . . . . . . . 154

9.2.3
EIFR - External Interrupt Flag Register . . . . . . . . . . . . . . . . . . . . . . . . . . 155

9.2.4
PCICR - Pin Change Interrupt Control Register . . . . . . . . . . . . . . . . . . 155

9.2.5
PCIFR - Pin Change Interrupt Flag Register . . . . . . . . . . . . . . . . . . . . . 155

9.2.6
PCMSK2 - Pin Change Mask Register 2 . . . . . . . . . . . . . . . . . . . . . . . . . 156

9.2.7
PCMSK1 - Pin Change Mask Register 1 . . . . . . . . . . . . . . . . . . . . . . . . . 156

9.2.8
PCMSK0 - Pin Change Mask Register 0 . . . . . . . . . . . . . . . . . . . . . . . . . 156

9.2.9
TIMSK0 - Timer/Counter0 Interrupt Mask Register . . . . . . . . . . . . . . . 157

9.2.10
TIFR0 - Timer/Counter0 Interrupt Flag Register . . . . . . . . . . . . . . . . . . 157

9.2.11
TIMSK1 - Timer/Counter1 Interrupt Mask Register . . . . . . . . . . . . . . . 158

9.2.12
TIFR1 - Timer/Counter1 Interrupt Flag Register . . . . . . . . . . . . . . . . . . 159

9.2.13
TIMSK2 - Timer/Counter2 Interrupt Mask Register . . . . . . . . . . . . . . . 159

9.2.14
TIFR2 - Timer/Counter2 Interrupt Flag Register . . . . . . . . . . . . . . . . . . 160