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Lecture 6 – Introduction to the
ATmega328 and Ardunio
C S E P567

Outline
? Lecture 6
? ATmega architecture and instruction set
? I/O pins
? Arduino C++ language
? Lecture 7
? ControllingTime
? Interrupts andTimers
? Lecture 8
? Guest lecture – Radio communication
? Lecture 9
? Designing PID Controllers

AVR Architecture
? Clocks and Power
? Beyond scope of this
course

AVR Architecture
? CPU
? Details coming

AVR Architecture
? Harvard architecture
? Flash – program memory
? 32K
? SRAM – data memory
? 2K
? EEPROM
? For long-term data
? O n I/O data bus

Memory
? Flash (32K) (15-bit addresses)
? Program memory – read only
? Non-volatile
? Allocate data to Flash using PROGMEM keyword
? see documentation
? SRAM (2K)
? T
emporary values,stack,etc.
? Volatile
? Limited space!
? EEPROM (1K)
? Long-term data
? see documentation on EEPROM library

AVR CPU
? Instruction Fetch
and Decode

AVR CPU
? I/O and special
functions

AVR Register File
? 32 8-bit GP registers
? Part of SRAM memory space

Special Addressing Registers
? X,Y and Z registers
? 16-bit registers made using registers 26 – 31
? Support indirect addressing

AVR Memory
? Program memory – Flash
? Data memory - SRAM

Addressing Modes
? Direct register
addressing

Addressing Modes
? Direct I/O addressing

Addressing Modes
? Direct data memory addressing

Addressing Modes
? Direct data memory with displacement addressing

Addressing Modes
? Indirect data memory addressing

Addressing Modes
? Indirect data memory addressing with pre-decrement

Addressing Modes
? Indirect data memory addressing with post-increment

Addressing Modes
? Program memory addressing (constant data)

Stack Pointer Register
? Special register in I/O space [3E,3D]
? Enough bits to address data space
? Initialized to RAMEND (address of highest memory address)
? Instructions that use the stack pointer

Program Status Register (PSR)
?
? Status bits set by instructions/Checked by Branch/Skip
instructions
? I – Global interrupt enable
? T – Flag bit
? H – Half carry (BCD arithmetic)
? S – Sign
? V – Overflow
? N – Negative
? Z – Zero
? C – Carry

Simple 2-Stage Pipeline
? Branch/Skip??

Single-Cycle ALU Instructions
? Most instructions execute in one cycle
? Makes program timing calculations (relatively) easy
? No cache misses
? 1 clock/instruction

Addressing Modes
? JMP
,CALL – Direct Program MemoryAddressing

Addressing Modes
? IJMP
,ICALL – Indirect program memory addressing

Addressing Modes
? RJMP
,RCALL – Relative program memory addressing

AVR Architecture
? Three timers
? Very flexible
? Choose clock rate
? Choose“roll-over” value
? Generate interrupts
? Generate PWM signals
? (represent 8-bit value with
using a clock signal)
? More in next lecture…

Arduino Timing Functions
? delay(ms)
? wait for ms milliseconds before continuing
? delayMicroseconds(us)
? wait for us microseconds before continuing
? unsigned long millis( )
? return number of milliseconds since program started
? unsigned long micros( )
? return number of microseconds since program started
? resolution of 4 microseconds

AVR Architecture
? Interface to pins
? Each pin directly
programmable
? Program direction
? Program value
? Program pull-ups
? Some pins are special
? Analog vs.Digital
? Clocks
? Reset

I/O Ports
? 3 8-bit Ports (B,C,D)
? 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)
? PINx – Pin input value
? Reading this “register” returns value of pin
? PO RTx – Pin output value
? Writing this register sets value of pin

Pin Input
DDRx = 0
off
PO RTx
PINx

Synchronization Timing
? Note:Takes a clock cycle for data output to be reflected
on the input

Pin Output
DDRx = 1
on
PO RTx
PINx

Pin Input – PORT controls pullup
DDRx = 0
off
PO RTx
PINx

I/O Ports
? Pullups
? If a pin is an input (DDRxi = 0):
? PO RTxi = 0 – pin is floating
? PO RTxi = 1 – connects a pullup to the pin
? Keeps pin from floating if noone driving
? Allows wired-OR bus
? Individual bits can be set cleared using bit-ops
? A bit can be toggled by writing 1 to PINxi
? SBI instruction e.g.

Arduino Digital and Analog I/O Pins
? Digital pins:
? Pins 0 – 7: PORT D [0:7]
? Pins 8 – 13:PO RT B [0:5]
? Pins 14 – 19:PORT C [0:5] (Arduino analog pins 0 – 5)
? digital pins 0 and 1 are RX andTX for serial communication
? digital pin 13 connected to the base board LED
? Digital Pin I/O Functions
? pinMode(pin,mode)
? Sets pin to INPUT or O UTPUT 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 PO RTx register
? int value = digitalRead(pin)
? Reads back pin value (0 or 1)
? Read 1 bit in the PINx register

Arduino Analog I/O
? Analog input pins:0 – 5
? Analog output pins:3,5,6,9,10,11 (digital pins)
? Analog input functions
? int val = analogRead(pin)
? Converts 0 – 5v
.voltage to a 10-bit number (0 – 1023)
? Don’t use pinMode
? analogReference(type)
? Used to change how voltage is converted (advanced)
? Analog output
? analogWrite(pin,value)
? value is 0 – 255
? Generates a PWM output on digital pin (3,5,6,9,10,11)
? @490Hz frequency

AVR Architecture
? Analog inputs
? Convert voltage to a
10-bit digital value
? Can provide reference
voltages

PWM – Pulse Width Modulation
? Use one wire to represent a multi-bit value
? A clock with a variable duty cycle
? Duty cycle used to represent value
? We can turn it into a analog voltage using an integrating filter

Port Special Functions
? Lots of special uses for pins
? Clock connections
? Timer connections
? e.g.comparator output for PWM
? Interrupts
? Analog references
? Serial bus I/O s
? USART
? PCI

Reading and Writing Pins Directly
? O nly one pin can be changed using theArduino I/O
functions
? Setting multiple pins takes time and instructions
? To change multiple pins simultaneously,directly read/write
the pin registers
? DDR{A/B/C}
? PORT{A/B/C}
? PIN{A/B/C}
? e.g.to set all digital pins 0 – 7 to a value:
? PORTD = B01100101;

AVR Architecture
? Special I/O support
? Serial protocols
? Uses special pins
? Uses timers
? Beyond scope of this
course

Arduino C Programs
? Arduino calls these“sketches”
? Basically C with libraries
? Program structure
? Header:declarations,includes,etc.
? setup()
? loop()
? Setup is likeVerilog initial
? executes once when program starts
? loop() is likeVerilog always
? continuously re-executed when the end is reached

Blink Program
int ledPin = 13; // LED connected to digital pin 13
// The setup() method runs once, when the sketch starts
void setup() {
// initialize the digital pin as an output:
pinMode(ledPin, OUTPUT);
}
// the loop() method runs over and over again,
// as long as the Arduino has power
void loop()
{
digitalWrite(ledPin, HIGH);
delay(1000);
digitalWrite(ledPin, LOW);
delay(1000);
}
// set the LED on
// wait for a second
// set the LED off
// wait for a second

The Arduino C++ Main Program
int main(void)
{
init();
setup();
for (;;)
loop();
return 0;
}

Arduino Serial I/O
? Communication with PC via USB serial line
? Use the Serial Monitor in the IDE
? Or set up a C or Java(or you-name-it) interface
? Example Serial library calls
? Serial.begin(baud-rate)
? 9600 default
? Serial.println(string)
? int foo = Serial.read()
? Read one byte (input data is buffered)
? See documentation for more

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Lecture6.pptx

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Lecture6.pptx