Lecture 2. Introduction to Microcontrollers

Transcription

1 Lecture 2 Introduction to Microcontrollers 1

2 Microcontrollers Microcontroller CPU Microprocessor CPU (on single chip) 2

3 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 4

5 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 and does not stand for anything in particular. The creators of the AVR give no definitive answer as to what the term "AVR" stands for. However, it is commonly accepted that AVR stands for Alf (Egil Bogen) and Vegard (Wollan)'s Risc processor" 5

6 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 Emphasis on hardware Include multi-clock complex instructions Memory-to-memory: Load and Store incorporated in instructions Small code sizes, high cycles per second Transistors used for storing complex instructions RISC Emphasis on software Include single-clock reduce instruction only Register-to-register: Load and Store are independent instructions Low cycles per second, large code sizes 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. 7

8 The AVR is a Harvard architecture CPU. Harvard Architecture AVR Microcontroller Computer architectures that used physically separate storage and signal pathways for their instructions and data. CPU can read both an instruction and data from at the same time that makes it faster. memory 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. 8

9 AVR Microcontroller Harvard Architecture Harvard Architecture diagram 9

10 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

11 AVR Basic Families AVRs are generally classified into six broad groups: tinyavr : megaavr XMEGA the ATtiny series (ATtinyXX) kb program memory 6 32-pin package Limited peripheral set the ATmega series (ATmegaXXX) pin package, 16kB kb program memory Extended instruction set (Multiply instructions and instructions for handling larger program memories) Extensive peripheral set the ATxmega series kb program memory pin package Extended performance features, such as DMA. Extensive peripheral set with DACs

12 AVR Basic Families Application-specific AVR megaavrs with special features not found on the other members of the AVR family, such as LCD controller, USB controller, advanced PWM, CAN (controller area network) AVR with FPGA FPGA 5K to 40K gates SRAM for the AVR program code, unlike all other AVRs AVR core can run at up to 50 MHz 32-bit AVRs Main article: AVR32 In 2006 Atmel released microcontrollers based on the new, 32- bit, AVR32 architecture. They include SIMD (Single instruction, multiple data, is a class of parallel computers) and DSP instructions, along with other audio and video processing features. This 32-bit family of devices is intended to compete with the ARM based processors. The instruction set is similar to other RISC cores, but is not compatible with the original AVR or any of the various ARM cores.

13 AVR Part Numbers ATmega168: 8-bit AVR Microcontroller, 16KB Flash, 28/32-pin ATmega328: 8-bit AVR Microcontroller, 32KB Flash, 28/32-pin ATmega2560: 8-bit AVR Microcontroller, 256KB Flash, 100-pin ATmega168 Atmel group Flash =16KB 13

14 ATmega328 Internal Architecture Internal memories 32KB Flash 1KB EEPROM 2KB SRAM Timer/Counter 8-bit CPU Universal Synchronous and Asynchronous serial Receiver and Transmitter (Serial) Serial Peripheral Interface GPIO 2-wire Serial Interface 14

15 AVR Architecture 15

16 1.Registers AVR Architecture 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

17 ATmegaxx8 Core Architecture 17

18 General Purpose Registers AVR Register File 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) 18

19 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

20 (SREG) 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). 20

21 (SREG) 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. 21

22 Program Counter Register(PC) Holds address of next program instruction to be executed. Automatically incremented when the ALU executes an instruction. The size (width) of the program counter of a microcontroller is measured in bits and is directly related to the size of the microcontroller's program memory(16-bits). 22

23 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

24 Special Function Registers 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) 24

25 Special Function Registers Address Name I/O Mem. $00 $20 TWBR $01 $21 TWSR $02 $22 TWAR $03 $23 TWDR $04 $24 ADCL $05 $25 ADCH $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 SPDR $10 $30 PIND $11 $31 DDRD $12 $32 PORTD $13 $33 PINC $14 $34 DDRC $15 $35 PORTC Address Name Address I/O Mem. I/O Mem. Name $16 $36 PINB $2B $4B OCR1AH $17 $37 DDRB $2C $4C TCNT1L $18 $38 PORTB $2D $4D TCNT1H $19 $39 PINA $2E $4E TCCR1B $1A $3A DDRA $2F $4F TCCR1A $1B $3B PORTA $30 $50 SFIOR $1C $3C EECR OCDR $1D $3D EEDR $31 $51 OSCCAL $1E $3E EEARL $32 $52 TCNT0 $1F $3F EEARH $33 $53 TCCR0 $20 $40 UBRRC $34 $54 MCUCSR UBRRH $35 $55 MCUCR $21 $41 WDTCR $36 $56 TWCR $22 $42 ASSR $37 $57 SPMCR $23 $43 OCR2 $38 $58 TIFR $24 $44 TCNT2 $39 $59 TIMSK $25 $45 TCCR2 $3A $5A GIFR $26 $46 ICR1L $3B $5B GICR $27 $47 ICR1H $3C $5C OCR0 $28 $48 OCR1BL $3D $5D SPL $29 $49 OCR1BH $3E $5E SPH $2A $4A OCR1AL $3E $5E SREG 25

26 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

27 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 memory Large permanent data storage.

28 Data Memory Space 28

29 Data Memory (RAM) In many AVR microcontrollers RAM is split into 4 subsections: General purpose registers. I/O registers (SFRs). Internal data SRAM. External data SRAM 29

30 Internal SRAM Internal data SRAM is widely used for storing data and parameters temporary by AVR programmers and C compilers. Each location of the SRAM can be accessed directly by its address. Each location is 8 bit wide and can be used to store any data we want. Size of SRAM is vary from chip to chip, even among members of the same family, ATmega328 has 2KB SRAM.. Memory is lost when power is shut off (volatile). Fast read and write. 30

31 Data Memory (EEPROM) 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 31

32 Program Memory (flash) Used to store program code. Memory contents retained when power is off (nonvolatile). 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. 16 bit Flash Memory Reset and interrupt vector section 42 words (84 bytes) Your programs go here! $3C00 32 $002A

33 EEPROM and Flash 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. 33

34 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 for windows environments. Place chip in final position and run

35 What is a Development Board A printed circuit board designed to facilitate work with a particular microcontroller. Typical components included in development board: power circuit programming interface basic input; usually buttons and LEDs I/O pins 35

36 The Arduino Development Board Arduino (The name is an Italian, meaning strong friend ) is an opensource 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. 36

37 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 Memory 32 KB (ATmega328) of which 2 KB used by bootloader SRAM 2 KB (ATmega328) EEPROM 1 KB (ATmega328) Clock Speed 16 MHz 37

38 ATmega328 Internal Architecture 38

39 ATmega328 Microcontroller Pin name Pin number Special function 39

40 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 be connected 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 pullupresistors 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]

41 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

42 Port Registers PORTB: PortB Data Register Bit DDRB: PortB Data Direction Register Bit PINB: Input Pins on PortB Bit Similar for Ports C and D.

43 Arduino Pin Mapping 43

44 ATmega168/328-Arduino Pin Mapping 44

45 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

46 Arduino Digital Pin I/O Functions 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. 46

47 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 t use 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, frequency, use pinmode(pin, OUTPUT); 47

48 Example/ Drive LED Arduino approach Alternate approach 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 } void setup() { DDRD = DDRD B ; // D5 } void loop() { PORTD = PORTD B ; delay(1000); PORTD = PORTD & B ; delay(1000); } 48

49 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

50 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 SRAM 50