Table of Contents

Introduction

Broad Overview of this Book

About the Targeted AVR Microcontrollers

Primary Programming Software

Why Learn Assembly Language?

The Many Reasons for Learning Assembly Language

C Programming

Intended Audience

Prerequisites

Software Requirements

Hardware Requirements

A DIP Packaged ATtiny

An Electronic Breadboard

Programmer/Debugger

Atmel-ICE Basic Kit

Atmel-ICE Full Kit

AVR Dragon

AVRISP mkII

Hobbyist USB Programmers

Power Supply

Jumper Links and Wires

Electronic Components

Optional Test Equipment

Microchip, Atmel, Microchip Studio and Atmel Studio

Accompanying Resources

Let’s Get Started

Chapter 1 • Overview of ATtiny Microcontrollers

1.1 ATtiny Microcontrollers

1.1.1 8-Pin Devices

1.1.1.1 ATtiny13 and ATtiny13A

1.1.1.2 ATtiny25, ATtiny45 and ATtiny85

1.1.2 14-Pin ATtiny24, ATtiny44 and ATtiny84

1.1.3 20-Pin Devices

1.1.3.1 ATtiny26

1.1.3.2 ATtiny261, ATtiny461 and ATtiny861

1.1.3.3 ATtiny2313 and ATtiny4313

1.1.4 28-Pin Devices

1.1.4.1 ATtiny48 and ATtiny88

1.1.4.2 ATtiny28L and ATtiny28V

1.2 Which ATtiny to Use

1.3 Comparison of ATtiny Devices

1.4 Summary

Chapter 2 • Hardware and Software Setup

2.1 Install Microchip Studio

2.1.1 Download Page and Software Version

2.1.2 Newest Software Version

2.1.3 Start the Installation

2.1.4 Installation Steps

2.2 8-Pin ATtiny Microcontroller LED Circuit

2.2.1 Circuit Power Supply

2.2.2 Decoupling Capacitor

2.3 A First Assembly Language Program

2.3.1 Start a New AVR Assembler Project in Microchip Studio

2.3.2 LED Blink Assembly Code

2.3.3 Build the Project

2.3.4 Fix Any Build Errors

2.3.5 Load the Program to the AVR Microcontroller

2.3.6 Fault Finding

2.4 A First C Program

2.4.1 Start a New GCC C Executable Project in Microchip Studio

2.4.2 LED Blink C Code

2.4.3 Build the Project

2.4.4 Fix Any Build Errors

2.4.5 Load the Program to the AVR Microcontroller

2.4.6 Fault Finding

2.5 Summary

Chapter 3 • Basics of Assembly Language

3.1 Mnemonics

3.2 AVR Instruction Set

3.3 Opcodes and Operands

3.4 Assembly Language Comments

3.5 LED Blink Program Operation

3.6 Using the Debugger and Simulator

3.6.1 Using the AVR Simulator and Debugger

3.6.2 Using a Physical AVR Microcontroller and Debugger

3.6.3 Putting an AVR Back into ISP mode

3.7 Summary

Chapter 4 • Binary Numbers and Memory

4.1 Bits and Bytes

4.1.1 Counting in Binary

4.1.2 Bytes and Nibbles

4.2 Weighted Number Systems

4.2.1 Weighted Decimal Numbers

4.2.2 Weighted Binary Numbers

4.3 Hexadecimal Numbers

4.3.1 Counting in Hexadecimal

4.3.2 Using Hexadecimal to Represent Binary

4.4 Calculating Number Sizes

4.4.1 Calculating the Maximum Value of a Binary Number

4.4.2 Calculating Memory Size

4.4.3 Converting Between Bytes and Kilobytes

4.5 Numbers in Assembly Programs

4.6 Numbers in C Programs

4.7 Summary

Chapter 5 • AVR Registers and Memory Map

5.1 AVR Registers

5.1.1 General Purpose Working Registers

5.1.2 I/O Registers

5.2 Using General Purpose Registers

5.2.1 Adding Two Registers

5.2.2 Incrementing a Register

5.3 AVR Memory Map

5.3.1 Program Memory

5.3.2 Data Memory

5.3.3 EEPROM

5.4 Accessing SRAM in Assembler Programs

5.4.1 SRAM Store and Load Example

5.4.2 Store and Load Example in the Simulator

5.4.3 SRAM Start Addresses

5.5 Summary

Chapter 6 • AVR Internal Architecture

6.1 Clock Pulses and Program Counter

6.1.1 Clock Pulses

6.1.2 Clock Pulse Period and Frequency

6.1.2.1 ATtiny13(A) Default Clock Frequency

6.1.2.2 ATtiny25/45/85 Default Clock Frequency

6.1.2.3 RC Oscillator Accuracy

6.1.2.4 Clock Sources and Improving Accuracy

6.1.2.5 Calculating Clock Period from Frequency

6.1.2.6 Calculating Clock Frequency from Period

6.1.3 The Program Counter

6.2 Microcontroller Buses

6.3 Harvard and von Neumann Architectures

6.4 Fetching and Executing Instructions

6.5 Status Register

6.5.1 Zero Flag

6.5.2 Negative Flag

6.6 Stack and Stack Pointer

6.6.1 How the Stack Works

6.6.2 Accessing the Stack with PUSH and POP

6.6.3 Calling a Subroutine

6.7 LED Blink Program Fully Explained

6.8 AVR Instruction Encoding

6.9 Addressing Modes

6.9.1 Register Direct Addressing

6.9.2 I/O Direct Addressing

6.9.3 Other Addressing Modes

6.10 Summary

Chapter 7 • Arithmetic and Logic Instructions

7.1 Positive and Negative Numbers

7.1.1 1’s Compliment Numbers

7.1.2 2’s Compliment Numbers

7.2 Addition

7.2.1 ADD – Add without Carry

7.2.2 ADC – Add with Carry

7.3 Subtraction

7.4 Logic Instructions

7.4.1 Logical AND

7.4.2 Logical OR

7.4.3 Logical Exclusive OR

7.5 Other Arithmetic and Logic Instructions

7.6 Summary

Chapter 8 • Programming AVR I/O Ports

8.1 Instructions for Accessing I/O Registers

8.1.1 Reading and Writing I/O Registers with IN and OUT

8.1.1.1 The IN Instruction

8.1.1.2 The OUT Instruction

8.1.2 I/O Register Bit Manipulation and Testing

8.1.3 Accessing I/O Registers as Data Space

8.2 I/O Ports

8.2.1 Configuring I/O Pins as Outputs in Assembler

8.2.1.1 Five LED 8-pin ATtiny Circuit

8.2.1.2 Using debugWIRE or ISP/SPI to Program an ATtiny AVR

Program-only Programmers

Peripheral Hardware Devices Interfering with Programming

Putting the AVR into debugWIRE Mode

8.2.1.3 Build the 5 LED ATtiny Circuit on Breadboard

8.2.1.4 Assembly Code for the 5 LED Count Circuit

8.2.1.5 Select the Debugger or Simulator

8.2.1.6 What the LED Count Assembler Code Does

8.2.1.7 Build and Run the Program

8.2.1.8 How the LED Count Assembler Program Works

8.2.1.9 Using a Breakpoint in the Debugger

8.2.2 Configuring I/O Pins as Outputs in C

8.2.2.1 LED Count C Code

8.2.2.2 How the LED Count C Code Works

8.2.2.3 Running the LED Count C Code

8.2.2.4 LED Count C Code Disassembly

8.2.3 Limiting a Count Value

8.2.4 Three Ways to Toggle an LED with an AVR

8.2.4.1 Toggling an LED by Value

8.2.4.2 Toggling an LED by Exclusive OR

8.2.4.3 Toggling an LED with the PINB Register

8.2.5 Configuring I/O Pins as Inputs

8.3 Summary

Chapter 9 • Assembly Language Elements

9.1 Instructions and Labels

9.2 The Preprocessor and Include Files

9.3 Assembler Directives

9.3.1 Specifying Code and Data Locations

9.3.1.1 ORG Assembler Directive

9.3.1.2 CSEG Code Segment Directive

9.3.1.3 DSEG Data Segment and BYTE Directives

9.3.1.4 ESEG EEPROM Segment Directive

9.3.2 Reserving Memory

9.3.2.1 BYTE

9.3.2.2 DB – Define Constant Byte

Modified Harvard Architecture

Example Code using the DB Assembler Directive

CSEG Directive and First RJMP Instruction

Usage of the DB Assembler Directive

Data Formats and Null Terminating Strings

Location of DB Data in Program Memory and Alignment

16-bit Address Pointer Registers

Loading the Z Register

Reading Bytes from Program Memory

Running the Example Code

9.3.2.3 DW – Define Constant Word

9.3.2.4 DD – Define Constant Double-word

9.3.2.5 DQ – Define Constant Quad-word

9.3.3 Defining Names for Registers with DEF

9.3.4 Equating Names to Expressions using EQU and SET

9.3.5 Conditional Assembly

9.4 Other Assembly Language Elements

9.5 Further Reading

9.6 Summary

Chapter 10 • AVR Timing, Timers and Interrupts

10.1 Instruction Timing

10.1.1 AVR CPU Versions

10.1.2 Instruction Timing Examples

10.1.2.1 The NOP Instruction

10.1.2.2 16-bit and 32-bit Instruction Timing

10.1.2.3 Timing of Branch Instructions

The Simulator Cycle Counter and Stop Watch

Simulator Cycle Counter Bug

10.2 Assembly Language Time Delay

10.2.1 Calculating a Software Delay Subroutine Time Delay

10.2.1.1 Delay Subroutine Cycle Counter Measurement

10.2.1.2 Delay Subroutine Mathematical Formula

10.2.2 A Better Software Delay Subroutine

10.2.2.1 Principle of Operation

10.2.2.2 32-bit Subtraction with 8-bit Registers

10.2.2.3 Timing of the Code

10.2.2.4 Testing the Code in Microchip Studio

10.2.3 A Changeable Software Time Delay Subroutine

10.2.3.1 Splitting an Assembly Language Project into Files

10.2.3.2 How the wait_ms Subroutine Works

10.2.3.3 Limits of the wait_ms Subroutine

Simplifying the Formula

Calculating the Maximum Delay Time of the Subroutine

Posing Value Limits in Assembly Language

Number Size Limits in the Assembler Program

Solution to Flagging Out of Range Upper Values

Flagging Out of Range High and Low Values

10.2.4 Passing a Value to a Subroutine

10.2.4.1 Simplest Way to Pass a Value

10.2.4.2 Improved Way to Pass a Value

10.3 Calling an Assembly Subroutine from C Code

10.3.1 Passing a Value to an Assembly Subroutine from C

10.3.1.1 Testing the wait_ms_c Project Code

10.3.1.2 How the wait_ms_c Project Code Works

10.3.2 Returning a Value from an Assembly Subroutine in C

10.4 Polled Timer Delay

10.4.1 Timer/Counter0 Registers

10.4.1.1 Timer/Counter0 Register Addresses

10.4.1.2 Using Counter/Timer0 as a Timer

10.4.2 Polled Timer Assembly Program

10.4.2.1 The IFNDEF Directive

10.4.2.2 Left Shift Operator

10.4.2.3 Register Write or Read-Modify-Write

10.4.2.4 Initializing Timer 0

10.4.2.5 Polling Timer 0

10.4.2.6 Running the Code in the Simulator

10.4.3 Polled Timer C Program

10.5 Timer Interrupt Delay

10.5.1 How Interrupts Work

10.5.2 The Interrupt Vector Table

10.5.3 Assembly Program Timer Interrupt

10.5.3.1 ATtiny13(A) Timer Interrupt Project

The Interrupt Vector Table

Main Program Code

Interrupt Service Routine Code

Running the Timer Interrupt Code

10.5.3.2 ATtiny25/45/85 Timer Interrupt Project

10.5.3.3 Universal Timer Interrupt Project

10.5.4 C Program Timer Interrupt

10.6 Summary

Chapter 11 • The AVR Instruction Set

11.1 AVR Instruction Set Overview and Categories

11.2 A Guided Tour through the ATtiny AVR Instruction Set

11.2.1 Arithmetic and Logic Instructions

11.2.1.1 Add and Subtract Instructions

Addition Instructions

Subtraction Instructions

11.2.1.2 Logical Instructions

Logical AND

Logical OR

Logical Exclusive OR

11.2.1.3 Increment and Decrement Instructions

11.2.1.4 Sign Change Instructions

11.2.1.5 Bit Set and Clear Instructions

11.2.1.6 Register Set, Clear and Test Instructions

11.2.2 Branch Instructions

11.2.2.1 Jump Instructions

11.2.2.2 Subroutine Call Instructions

11.2.2.3 Return from Subroutine and Interrupt Instructions

11.2.2.4 Compare Instructions

11.2.2.5 Skip Instructions

11.2.2.6 Branch Instructions

Branch if Bit in SREG Set or Cleared

Branch if Equal or Not Equal – SREG Z Flag

Branch if Carry Set or Cleared – SREG C Flag

Branch if Same or Higher, or Lower – SREG C Flag

Branch if Minus or Plus – SREG N Flag

Branch if Greater or Equal, or Less Than Signed – SREG S Flag

Branch if Half Carry Flag Set or Cleared – SREG H Flag

Branch if T Bit Set or Cleared – SREG T Flag

Branch if Overflow Flag Set or Cleared – SREG V Flag

Branch if Interrupt Enabled or Disabled – SREG I Flag

11.2.3 Bit and Bit-test Instructions

11.2.3.1 Bit Set and Clear Instructions

11.2.3.2 Shift, Rotate and Swap Instructions

Logical Shift Instructions

Rotate through Carry Instructions

Logical Shift and Rotate Code Example

Led Chaser Logical Shift Code Example

Arithmetic Shift and Swap Instructions

11.2.3.3 Status Register Bit Set and Clear Instructions

Set or Clear SREG Bit

Store or Load SREG T Bit to/from Register

Set or Clear Carry Flag – SREG C Bit

Set or Clear Negative Flag – SREG N Bit

Set or Clear Zero Flag – SREG Z Bit

Set or Clear Global Interrupt Flag Bit – SREG I Bit

Set or Clear Sign Flag – SREG S Bit

Set or Clear Two’s Compliment Overflow Flag – SREG V Bit

Set or Clear T Bit in SREG – SREG T Bit

Set and Clear Half Carry Flag – SREG H bit

11.2.4 Data Transfer Instructions

11.2.4.1 Move/Copy Instructions

11.2.4.2 Load Immediate Instruction

11.2.4.3 Load Indirect Instructions

11.2.4.4 Store Indirect Instructions

11.2.4.5 Load Indirect with Displacement

11.2.4.6 Store Indirect with Displacement

11.2.4.7 Load Direct from SRAM

11.2.4.8 Store Direct to SRAM

11.2.4.9 Load Program Memory Instructions

11.2.4.10 Store Program Memory

11.2.4.11 Port IN and OUT Instructions

11.2.4.12 PUSH and POP Instructions

11.2.5 MCU Control Instructions

11.3 Entire AVR Instruction Set

11.3.1 Number of AVR Instructions

11.3.1.1 Total Number of AVR Instructions

11.3.1.2 Number of ATtiny AVR Instructions

11.3.1.3 Discrepancies in Documentation

11.3.2 Other AVR Instructions

11.3.2.1 Arithmetic and Logic Instructions

11.3.2.2 Branch Instructions

11.3.2.3 Data Transfer Instructions

11.3.3 Putting Instructions into Perspective

11.3.3.1 The Full AVR Instruction Set

11.3.3.2 The Plain AVR CPU

11.3.3.3 Reduced AVRrc Core

11.3.3.4 AVRe and AVRxt Cores

11.3.3.5 AVRe+ CPU

11.3.3.6 AVRxm CPU

Chapter 12 • Software Tools and Settings

12.1 AVR Assembler Programs

12.1.1 The AVRASM2 Assembler

12.1.1.1 Building a Project with AVRASM2

12.1.1.2 AVRASM2 on the Command Line

12.1.1.3 AVRASM2 Options in Microchip Studio

12.1.1.4 List File Options

12.1.2 The AVR-AS Assembler

12.1.3 The AVRA Assembler

12.2 The GNU C Toolchain

12.3 Where to from Here?

12.3.1 Objectives Achieved

12.3.2 What was Not Covered

12.3.3 Other AVR Microcontrollers

12.3.4 Assembly Language Resources

Appendix A • External Programmer Setup

Appendix B • Alternate Circuits and Programs

Appendix C • The ASCII Table

Index