Introduction to Microcontrollers

Lecture 2

1

Microcontroller

CPU + ++++++++++

Microprocessor

CPU (on single chip)

Microcontrollers

2

What is a Microcontroller Integrated chip that typically contains integrated CPU, memory (RAM

ROM), I/O ports on a single Chip.

System on a single Chip/ small computer on a single chip.

Designed to execute a specific task to control a single system.

Differs from Microprocessor

general-purpose chip

Used to design multi purpose computers or devices

Require Multiple chips to handle various tasks

Typically Microcontroller embedded inside some device.

Microcontrollers are important part of Embedded systems.

Abbreviated µC, uC or MCU.

3

4

Microcontroller Families

68H12: Motorola 68H11, 68HC12, …

8051: Intel 8051, 8052, 80251,…

PIC: Microchip PIC16F628, 18F452, 16F877, …

AVR: Atmel ATmega128, ATtiny28L, AT90S8515,…

We are going to look at AVR

AVR Microcontroller

AVR architecture was conceived by two students(Alf

Egil Bogen & Vegard Wollan RISC ) at Norwegian

Institute of Technology (NTH) and further refined and

developed at Atmel Norway (Atmel AVR).

Atmel says that the name AVR is not an acronym anddoes not stand for anything in particular. The creators ofthe AVR give no definitive answer as to what the term"AVR" stands for. However, it is commonly accepted thatAVR stands for Alf (Egil Bogen) and Vegard (Wollan)'sRisc processor"

5

AVR Microcontroller

AVR Microcontrollers is Family of RISC

Microcontrollers from Atmel.

There are multiple architectures

RISC (Reduced Instruction Set Computer)

CISC (Complex Instruction Set Computer)

6

7

RISC versus CISC

CISC RISC

Emphasis on hardware Emphasis on software

Include multi-clock complex instructions Include single-clock reduce instruction only

Memory-to-memory: “Load” and “Store” incorporated in instructions

Register-to-register: “Load” and “Store” are independent instructions

Small code sizes, high cycles per second Low cycles per second, large code sizes

Transistors used for storing complex instructions

Spends more transistors on memory registers

Most PC's use CPU based on CISC architecture. For instance

Intel and AMD CPU's are based on CISC architectures.

Apple is based on RISC architecture.

The AVR is a Harvard architecture CPU.

Harvard Architecture

Computer architectures that used physically separate storage and signal pathways for their instructions and data.

CPU can read both an instruction and data from memory at the same time that makes it faster.

von Neumann architecture

CPU can Read an instruction or data from/to the memory.

Read, Write can`t occur at the same time due to same memory and signal pathway for data and instructions.

AVR Microcontroller

8

Harvard Architecture

AVR Microcontroller

Harvard Architecture diagram

9

AVR Microcontroller

AVR is a family of 8-bit microntrollers with a large range of variants

differing in:

- Size of program-memory [ Flash]

- Size of EEPROM memory [store long-term information.]

- Size of SRAM [variables]

- Number of I/O pins

- Number of on-chip features such as UART and ADC

Smallest microcontroller is the ATTiny11

Large such as the ATMEGA328

10

AVRs are generally classified into six broad groups:

tinyAVR : the ATtiny series (ATtinyXX) 0.5–8 kB program memory 6–32-pin package Limited peripheral set

megaAVR the ATmega series (ATmegaXXX) 28–100-pin package, 16kB - 128 kB program memory Extended instruction set (Multiply instructions and instructions for handling larger program memories) Extensive peripheral set

XMEGA the ATxmega series 16–384 kB program memory 44–64–100-pin package Extended performance features, such as DMA. Extensive peripheral set with DACs

AVR Basic Families

Application-specific AVRmegaAVRs with special features not found on the othermembers of the AVR family, such as LCD controller, USB

controller, advanced PWM, CAN (controller area network)

AVR with FPGAFPGA 5K to 40K gatesSRAM for the AVR program code, unlike all other AVRsAVR core can run at up to 50 MHz

32-bit AVRsMain article: AVR32In 2006 Atmel released microcontrollers based on the new, 32-

bit, AVR32 architecture. They include SIMD (Singleinstruction, multiple data, is a class of parallelcomputers) and DSP instructions, along with other audio and

video processing features. This 32-bit family of devices isintended to compete with the ARM based processors. Theinstruction set is similar to other RISC cores, but is notcompatible with the original AVR or any of the various ARMcores.

AVR Basic Families

13

AVR Part Numbers

ATmega168

Atmel groupFlash =16KB

ATmega168: 8-bit AVR Microcontroller, 16KB Flash, 28/32-pinATmega328: 8-bit AVR Microcontroller, 32KB Flash, 28/32-pinATmega2560: 8-bit AVR Microcontroller, 256KB Flash, 100-pin

ATmega328 Internal Architecture

14

8-bit CPU

Timer/Counter

Internal memories

32KB Flash

1KB EEPROM

2KB SRAM

Serial Peripheral InterfaceUniversal Synchronous

and Asynchronous serial Receiver and Transmitter (Serial)

GPIO 2-wire Serial Interface

AVR Architecture

15

AVR Architecture1.Registers

Two types of registers

General purpose & Special purpose registers

General purpose registers

32 general purpose registers

Having storage capacity of 8-Bits

Named as R0 to R31.

Can store both Data & Addresses.

Special purpose I/O registers : Three

Program counter (PC)

Stack Pointer (SP)

Status Register (SREG)

*Other I/O registers called SFRs 16

ATmegaxx8 Core Architecture

17

18

General Purpose Registers

• There are 32 8-bit GPR R0-R31– Used as accumulators – for most

math and logic

• X, Y, Z are 16-bit registers that overlap R26-R31– Used as address pointers

– Or to contain larger values (>255)

AVR Register File

Status Register (SREG)

Contains information about the result of the most

recently executed arithmetic instruction.

Information can be used for altering program flow

in order to perform conditional operations.

Updated after any of ALU operations by hardware.

19

(SREG)

20

Bit 7 – I: Global Interrupt Enable

Used to enable and disable interrupts, 1: enabled. 0: disabled.

The I-bit is cleared by hardware after an interrupt has occurred, and is set by the

RETI instruction to enable subsequent interrupts.

Bit 6 – T: Bit Copy Storage

The Bit Copy instructions; BLD (Bit LoaD) and BST (Bit STore) use the T-bit as

source or destination for the operated bit. A bit from a register in the Register File

(GPR) can be copied into T by the BST instruction, and a bit in T can be copied

into a bit in a register in the Register File by the BLD instruction.

Bit 5 – H: Half Carry Flag

The Half Carry Flag H indicates a Half Carry (carry from bit 4) in some arithmetic

operations.

Half Carry is useful in BCD arithmetic.

Bit 4 – S: Sign Bit

Exclusive OR between the Negative Flag N and the Two’s Complement Overflow

Flag V ( S = N ⊕V).

(SREG)

21

Bit 3 – V: Two’s Complement Overflow Flag

The Two’s Complement Overflow Flag V supports two’s complement arithmetic.

Bit 2 – N: Negative Flag

N is the most significant bit of the result.

Bit 1 – Z: Zero Flag

Z indicates a zero result in an arithmetic or logic operation. 1: zero. 0: Non-zero.

Bit 0 – C: Carry Flag

Set if there was carry from the MSB of the result; cleared otherwise.

Program Counter Register(PC)

Holds address of next program instruction tobe executed.

Automatically incremented when the ALUexecutes an instruction.

The size (width) of the program counter of amicrocontroller is measured in bits and isdirectly related to the size of themicrocontroller's program memory(16-bits).

22

Stack Pointer (SP)

In AVR, a stack is implemented as a block of

consecutive bytes in the SRAM memory.

The Stack is mainly used for storing

temporary data, for storing local variables and

for storing return addresses after interrupts

and subroutine calls.

The Stack Pointer Register (16-bits) stores a

pointer to a group of data known at the stack

and always points to the top of the Stack.23

Special Function Registers

24

The I/O memory is dedicated to specific functions such as

timers, serial communication, I/O ports, ADC and etc.

Function of each I/O memory location is fixed by the CPU

designer at the time of design. (because it is used for control of

the microcontroller and peripherals)

AVR I/O memory is made of 8 bit registers.

All of the AVRs have at least 64 bytes of I/O memory location.

(This 64 bytes section is called standard I/O memory)

In other microcontrollers, the I/O registers are called SFRs

(Special Function Registers)

25

NameAddressI/O Mem.

$00 $20 TWBR

$01 $21 TWSR

$04 $24 ADCL

$05 $25 ADCH

$02 $22 TWAR

$03 $23 TWDR

$06 $26 ADCSRA

$07 $27 ADMUX

$08 $28 ACSR

$09 $29 UBRRL

$0A $2A UCSRB

$0B $2B UCSRA

$0C $2C UDR

$0D $2D SPCR

$0E $2E SPSR

$0F $2F

PIND$10 $30

DDRD$11 $31

PORTD$12 $32

PINC$13 $33

DDRC$14 $34

PORTC$15 $35

PINB$16 $36

DDRB$17 $37

PORTB$18 $38

PINA$19 $39

DDRA$1A $3A

PORTA$1B $3B

EECR$1C $3C

EEDR$1D $3D

EEARL$1E $3E

EEARH$1F $3F

SPDR

NameAddressI/O Mem.

NameAddressI/O Mem.

UBRRC$20 $40

UBRRH

$21 $41 WDTCR

$22 $42 ASSR

$23 $43 OCR2

$24 $44 TCNT2

$25 $45 TCCR2

$26 $46 ICR1L

$27 $47 ICR1H

$28 $48 OCR1BL

$29 $49 OCR1BH

OCR1AH$2B $4B

SFIOR$30 $50

OCDR$31 $51

OSCCAL

$32 $52

TCCR0$33 $53

MCUCSR$34 $54

MCUCR$35 $55

TWCR$36 $56

SPMCR$37 $57

TIFR$38 $58

TIMSK$39 $59

TCNT1L$2C $4C

TCNT1H$2D $4D

TCCR1B$2E $4E

TCCR1A$2F $4F

TCNT0

$3A $5A

GICR$3B $5B

OCR0$3C $5C

SPL$3D $5D

SPH$3E $5E

GIFR

OCR1AL$2A $4A SREG$3E $5E

Special Function Registers

I/O Memory Registers

• SREG: Status Register

• SP: Stack Pointer Register

• GIMSK: General Interrupt Mask Register

• GIFR: General Interrupt Flag Register

• MCUCR: MCU General Control Register

• MCUSR: MCU Status Register

• TCNTO: Timer/Counter 0 Register

• TCCR0A: Timer/Counter 0 Control Register A

• TCCR0B: Timer/Counter 0 Control Register B

• OCR0A: Timer/Counter 0 Output Compare Register A

• OCR0B: Timer/Counter 0 Output Compare Register B

• TIMSK0: Timer/Counter 0 Interrupt Mask Register

• TIFR0: Timer/Counter 0 Interrupt Flag Register

• EEAR: EEPROM Address Register

• EEDR: EEPROM Data Register

• EECR: EEPROM Control Register

• PORTB: PortB Data Register

• DDRB: PortB Data Direction Register

• PINB: Input Pins on PortB

• PORTD: PortD Data Register

• DDRD: PortD Data Direction Register

• PIND: Input Pins on PortD

• SPI I/O Data Register

• SPI Status Register

• SPI Control Register

• UART I/O Data Register

• UART Status Register

• UART Control Register

• UART Baud Rate Register

• ACSR: Analog Comparator Control and Status Register

2. AVR Memory

Three parts, each has its own address space:

Data memory Storing data to be processed.

Program memory (flash) Storing program and

sometimes constants.

EEPROM memoryLarge permanent data storage.

Data Memory Space

28

Data Memory (RAM)

General purpose registers.

I/O registers (SFRs).

Internal data SRAM.

External data SRAM

29

In many AVR microcontrollers RAM is split into 4 subsections:

Internal SRAM

30

Internal data SRAM is widely used for storing data andparameters temporary by AVR programmers and Ccompilers.

Each location of the SRAM can be accessed directly by itsaddress.

Each location is 8 bit wide and can be used to store anydata we want.

Size of SRAM is vary from chip to chip, even amongmembers of the same family, ATmega328 has 2KB SRAM.

.Memory is lost when power is shut off (volatile).

Fast read and write.

Data Memory (EEPROM)

31

8-bit EEPROM memory.

ATmega328 contains 1024 bytes.

Different chip have different size of

EEPROM.

Typically reserved for variables that

must retain their value in the event of

a shutdown (non-volatile) (e.g., system

calibration data unique to each board).

Fast read; slow write. Can write individual bytes.

Can be accessed using load and store

instructions with special control bit

settings

Program Memory (flash)

32

16 bit Flash Memory Used to store program code.

Memory contents retained when power is off (non-volatile).

Size dependent on AVR microcontroller

Read-only memory (writing is external to code).

Can only write entire “blocks” of memory at a time.

Fast to read; slow to write.

ATmegaxx8, there are 32KB of program memory (Flash memory)

Organized as 16K 2-byte words

Because program instructions are either 2(common) or 4 (less common) bytes long

Each word (not byte) in Flash memory has a unique address

Beginning address $0000

Ending address $3FFF

Some Flash memory is reserved or protected.

First 42 words (reserved)

bootloader sizes differs from 0.5 to 8 KB for different boards.

$3C00

Reset and interrupt vector section

42 words (84 bytes)

$002A

Your programs go here!

33

The main difference between EEPROM and Flash is the type of logic gates

that they use.

While EEPROM uses the faster NOR , Flash uses the slower NAND type.

The NOR type is a lot faster than the NAND type but there is the matter of

affordability as the former is significantly more expensive than the NAND

type.

Summary:

1.Flash is just one type of EEPROM

2.Flash uses NAND type memory while EEPROM uses NOR type

3.Flash is block-wise erasable while EEPROM is byte-wise erasable

4.Flash is constantly rewritten while other EEPROMs are seldom rewritten

5.Flash is when large amounts are needed while EEPROM is used when

only small amounts are needed.

EEPROM and Flash

Programming AVR Write your program (AVR Studio)

Debug in Simulator mode

Create .hex code

Transfer code to Chip

Connect USB Programmer (AVRISP MKII) to computer and breadboard

Use AVR Studio to download program

AVR Studio: Integrated Development Environment(IDE) for writing and debugging AVR applications forwindows environments.

Place chip in final position and run

What is a Development Board

A printed circuit boarddesigned to facilitatework with a particularmicrocontroller.

• Typical components included in development board:• power circuit • programming interface• basic input; usually buttons and LEDs• I/O pins

35

The Arduino Development Board

36

Arduino (The name is an Italian , meaning “strong friend”) is an open-

source platform used for building electronics projects. Arduino consists of both a

physical programmable circuit board (often referred to as a microcontroller) and a

piece of software, or IDE (Integrated Development Environment) that runs on your

computer, used to write and upload computer code to the physical board.

Arduino Microcontroller Boards

Microcontroller ATmega328

Operating Voltage 5 V

Input Voltage

(recommended)7-12 V

Input Voltage (limits) 6-20 V

Digital I/O Pins 14 (of which 6 provide PWM output)

Analog Input Pins 6

DC Current per I/O Pin 40 mA

DC Current for 3.3V Pin 50 mA

Flash Memory32 KB (ATmega328) of which 2 KB used by

bootloader

SRAM 2 KB (ATmega328)

EEPROM 1 KB (ATmega328)

Clock Speed 16 MHz

37

ATmega328 Internal Architecture

38

ATmega328 Microcontroller

Pin numberPin name

Special function

39

Pins and Ports Overview GND: Ground (0V) VCC: Digital Supply Voltage (2,7 – 5,5V) AVCC: In Arduino Uno and ArduinoMega2560, this pin was simply connected

to VCC. According to the atmel datasheet, this pin should beconnected to a Low-Pass filter when the ADC converted is used.

AREF: Analog Reference Voltage, usually VCC. /Reset: Low level on this pin will generate a reset

Port B, Port C, Port D:

• The communication channels through which information flows into or

out of the microcontroller.

• General Purpose 8 Bit bidirectional I/O Ports, optional internal pullup-

resistors when configured as input, output source capability 20mA.

Special Functions of the Ports available as configured using the SFRs:

Port D: UART, External Interrupts, Analog Comparator. [8 bits]Port B: External Oscillator/Crystal, SPI. [8 bits]Port C: A/D converters, TWI. [7 bits]

Pins and Ports Overview All the work of MCU happens through registers

(special memory locations).

Each port controlled by 3 8-bit registers.

Each bit controls one I/O pin. DDRx: Direction register, defines whether a pin is an input (0)

or and output (1), x denotes the port. DDRB = 0x02; /* sets the

second lowest of port B to output”.

PINx: Pin input value, reading this register returns value of pin.

unsigned int x= PINB; /* Places the status of port B into variable

x */.

PORTx: Pin output value, writing this register sets value of pin.

PORTB = 0x02; /* sets the second bit of port B and clears the

others */ 41

Port Registers

PORTB: PortB Data Register

DDRB: PortB Data Direction Register

PINB: Input Pins on PortB

Bit 7 6 5 4 3 2 1 0

Bit 7 6 5 4 3 2 1 0

Bit 7 6 5 4 3 2 1 0

Similar for Ports C and D.

Arduino Pin Mapping

43

ATmega168/328-Arduino Pin Mapping

44

Arduino Digital and Analog I/O Pins

Digital pins:

• Pins 0 – 7: PORT D [0:7]

• Pins 8 – 13: PORT B [0:5], 6&7 XTAL

• Digital pins 0 and 1 are RX and TX for

serial communication.

• Digital pin 13 connected to the base

board LED.

Analog pins:

• Arduino analog pins (0 – 5) : PORT C

[0:5] , 6 reset 45

Arduino Digital Pin I/O Functions

46

pinMode(pin, mode); Sets pin to INPUT or OUTPUT mode. Writes 1 bit in the DDRx register.

digitalWrite(pin, value); Sets pin value to LOW or HIGH (0 or 1). Writes 1 bit in the PORTx register.

int value = digitalRead(pin); Reads back pin value (0 or 1). Read 1 bit in the PINx register.

Arduino Analog Pin I/O Functions

Analog input pins: 0 – 5 .

Analog output pins: 3, 5, 6, 9, 10, 11 (digital pins) .

Analog input function:

• int val = analogRead(pin), converts (0-5)voltage to a 10-bit number (0 – 1023), don’tuse pinMode, Pin=A0, or Ax.

Analog output function:

• analogWrite(pin, value), value is (0-255),Generates a PWM output on digital pin (3, 5,6, 9, 10, 11) @490Hz frequency, usepinMode(pin, OUTPUT); 47

Example/ Drive LED

48

int myPin = 5; // Arduino digital pin 5

void setup()

{

pinMode(myPin,OUTPUT);

}

void loop()

{

digitalWrite(myPin,HIGH);

delay(1000); //ms

digitalWrite(myPin,LOW);

delay(1000 ); //ms

}

Arduino approach Alternate approach

void setup()

{

DDRD = DDRD | B00100000; // D5

}

void loop()

{

PORTD = PORTD | B00100000;

delay(1000);

PORTD = PORTD & B11011111;

delay(1000);

}

Problem with SRAM size

For example: string

char message[] = "I support the Cape

Wind project.";

Which equals to 33 bytes into SRAM (each

character takes a byte, plus the '\0'

terminator).

If you run out of SRAM, your program

may fail in unexpected ways.

49

To solve this problem

If your sketch talks to a program running on a

(desktop/laptop) computer, you can try shifting

data or calculations to the computer, reducing the

load on the Arduino.

If you have lookup tables or other large arrays,

use the smallest data type necessary to store the

values you need; for example, an int takes up two

bytes, while a byte uses only one (but can store a

smaller range of values).

If you don't need to modify the strings or data

while your sketch is running, you can store them

in flash (program) memory instead of SRAM50