Our local instructor this week was Juha Mäkelä

To Do

  1. Read the ATtiny44A data sheet
  2. from week 7
  3. Group work

The "Doing"

ATtiny44A data sheet

Note: The following information is extracted from the ATtiny44a data sheet.
ATtiny44A is a High Performance, Low Power AVR® 8-bit Microcontroller that has

  • Advanced RISC Architecture
  • 32x8 General Purpose Working Registers
  • 12 programmable I/O Lines (8 + 4)
  • Operating Voltage 1.8 to 5.5V
Pinout ATtiny44A
Pinout ATtiny44A
Description of some of the pins:
  • PB3:PB0 -> bi-directional I/O port
  • PB3 has RESET capability.
    • to use as I/O, program ('0') RSTDISBL fuse
  • As inputs, Port B pins that are externally pulled low will source current if the pull-up resistors are activated.
  • PA7:PA0 -> 8 bi-directional I/O port
  • As inputs, Port A pins that are externally pulled low will source current if the pull-up resistors are activated.
  • A low level on this pin for longer than the minimum pulse length will generate a reset

Programming the board

Understanding Registers & Programming

Writing/Reading from registers

  • A pin is set => 1
  • A pin is clear => 0

  • DDRA/DDRB (Data Direction register): Define the direction of a pin

    • If a bit in the DDR is set (1), that pin is an output
      • Write to an output pin using: PORTA/PORTB
    • If a bit in the DDR is clear (0), that pin is an input
      • Read from an input pin: PINA/PINB
Bit operators in C
  • ~ NOT
  • & AND
  • | OR
  • ^ XOR
Set Bit j:
  • R = R | (1 << j)
Clear Bit j:
  • R = R & ~(1 << j)
Check bit j
  • R & (1 << j)
Flip Bit j:
  • R = R ^ (1 << j)

Programming with AtMel Studio

In week 7 (Electronics design) I already used AtmelStudio for compiling and program my board. I start by creating a new project

new project
File > New Project
device selection
Device selection: ATtiny44A
Empty main.c created
Then, I think what I want to do. I want to light the led from my board when the button is pressed. I check from my schematics of the board from assignment 7 the information I need:
  • Led is connected to PB2 (Leg 5)
    • Led is an output device => Set bit in DDRB
    • Led will light up when output PB2 is set => set PB2 of PORTB
  • Switch is connected to PA7 (Leg 6)
    • Switch is an input device => Clear bit in DDRA
    • When switch is pressed, input PA7 is GRND => read value of PA7 of PINA is 0
Schematic of the board (from assignment 7)
Now, I just need to code that information in C, load it with Atmel and avrdude (as explained in week 7), and test it:
button and Led in C
Program in C
press button
Pressing the button

Programming with Arduino IDE

First, download Arduino IDE and install it. Then, we need to add support for ATtiny44A board in Arduino IDE. For that:

  • Open Arduino IDE
  • (Figure on the Right) In File > Preferences, add to Additional Boards Manager URLs the URL https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json
  • Then, in Tools > Board:xxx >Boards Manager scroll to the bottom and click install press button
press button
Support for ATtiny44
Now, in Tools > Board:xxx we can select ATtiny44A , and put the correct settings (Board: ATtiny24/44/84, Processor: ATtiny44, Clock: External 20 MHz, Port: COM4, Programmer: USBtinyISP) as shown below, before executing Burn Bootloader (that is, programming fuses => Connect the board!!!) correct settings
Correct settings before Burn Bootloader
I will do the same program as before. As suggested by Antti, I open an example for Arduino for a button and a LED at File > Examples > 02.Digital > Button. This example is for Arduino, so the PINS are for it. We need to know the matching pins. From the image bellow and comparing with the pinout of ATtiny on the top of the page:
  • Button -> PA7 -> leg 6 -> PIN7
  • LED -> PB2 -> leg 5 -> PIN8
press button
Pins matching ARduino - ATtiny44
Then I just need to
  • changing the PINs accordingly and also check the switch when it is LOW,
  • Upload the code (with the arrow on the top of the file)
  • Test!
button and Led in Arduino
Change and upload Program in Arduino
press button
Pressing the button
release button
Releasing the button

Programming with Assembler

As I had some time left, and hoping it will not get much time either, I have decided to give it a try. Why? I know that if I do not try now, I won't try this later. Moreover, I had to program in assembler a long looong time ago, so this is an exercise of "how much do you remember?" At this point, I would say that nothing (tags, registers, jumps...). Let's see!
First thing for me is prepare the environment. I noticed in ATmel studio, when creating a new project, I could choose to create an AVR Assembler Project. File > New Project Select Assembler > AVR Assembler Project

new project
File > New Project
device selection
Device selection: ATtiny44A
Empty main.asm created
Now, what do I want to do? I think I will simplify the functionality. I will be happy if I just could switch on and off the led. So, what do I need?
  • I need to know how to write in the registers
  • I need to know how to do a routine for a delay
    • decrement a register?
    • loop
  • I need to know how to jump to a loop
There is another option, that is using interruptions, but I found an example for ATmega8 at AVRBeginners for a delay routine, and I follow it. This helps to narrow some directives and instructions (the information of this is in the data sheets > Instruction Set Summary ):
  • .cseg: code segment
  • .dseg: data segment
  • LDI R, value: load register with value
  • CLR R: Clear register
  • OUT P, R: Out Port with R
  • DEC R: Decrement register
  • .org $000: Initialize the stack pointer
  • SBI P, b: Set bit in I/O register
  • CBI P, b: Clear bit in I/O register
  • ADIW R,k: add immediate to word (affects R and higher R. Eg, R=R4, affects R25 also as high of the word)
  • BRNE k: Branch if Not Equal
  • RJMP k: Relative jump
  • RCALL k: Relative subroutine call. Remembers the origin for RET
  • RET k: Subroutine return
Things to take into consideration for calculating a loop delay of 0,5 secs, according to example for ATmega8 at AVRBeginners. The calculations are done for 4MHz (note our board is working 20MHz):
  • 1 clock cycle: 0.00000025 seconds
  • Some durations:
    • 1 clock cycle: SBI, CBI, CLR, BRNE (if branch not done), LDI, DEC
    • 2 clock cycles: ADIW, BRNE (if branch done)
  • A delay of 0.5 seconds at 4 MHz equals 2,000,000 clock cycles (which means a delay of 0,1 seconds in my board)
  • AVR is an 8-bit microcontroller, the registers con only hold the values 0 to 255
  • But!! Registers can be used in pairs=>values from 0 to 65535. The following piece of code clears registers 24 and 25 and increments them in a loop until they overflow to zero again. When that condition occurs, the loop doesn't go around again:
    clr r24
    clr r25
          adiw r24, 1
          brne delay_loop
    • Loop without overflow: ADIW(2) + BRNE(2) = 4 cycles. This is done 0xFFFF times before the overflow occurs.
    • The next time the loop only needs 3 cycles, because no branch is done
    • This adds up to 4*0xFFFF(looping) + 3(overflow) + 2(CLR) = 262145 cycles. Which means: 2,000,000/262,145 ~ 7.63
  • We need to create a loop "around" that loop which will contain our 262,145 cycle loop.
    • For fine-tuning the inner loop we need to change the CLR instructions to LDI so that we can use a different start value than 0.
    • The "outer" loop will be down-counting from 8 (7 would not be enough, see later) to zero using r16. This is how the delay code looks now:
    ldi r16, 8
        ldi r24, 0
        ldi r25, 0
        adiw r24, 1
        brne delay_loop
        dec r16
        brne outer_loop
  • The inner loop is now treated like one BIG instruction needing 262,145 clock cycles. LDI needs 1 clock cycle, DEC also needs 1 clock cycle and BRNE needs 1 or 2 cycles .
  • The overall loop needs: 262,145 (inner loop) + 1 (DEC) + 2 (BRNE) = 262148 * 8 = 2097184 cycles plus the initial LDI = 2097185 . Wait. Subtract one because the last BRNE didn't result in a branch, so it needs 2097184 cycles. (Note, if r16 would down-count from 7 => 262148 * 7 = 1835036 cycles plus 1, not enough)
    • This is more like what we want, but 97184 cycles too long. This is where the fine-tuning comes in - we need to change the initial value of r24:r25.
  • The outer loop is executed 8 times and includes the "big-inner-loop-instruction". We have to subtract some cycles from the inner loop: 97184 / 8 =12148 cycles per inner loop. This is what the inner loop has to be shorter. Every iteration of the inner loop takes 4 cycles (the last one takes 3 but that's not so important), so let's divide those 12148 by 4. That's 3036.5 or 3037 less iterations. This is our new initialization value for r24:r25!
The final program looks like: new project
Assembler code


Once done


  • I have read a bit more (not all) the ATtiny44a data sheets
  • I have reviewed some C for handling registers and bits
  • I have generated some short C code for my hello board
  • I have programmed my hello board again with ATMStudio
  • I have downloaded and get first contact with ARDUino
  • I have programmed my hello board with Arduino IDE
  • I have programmed my hello board with Assembly language


  • I was a bit lost, as I could not attend the introductory class by our local instructor. And I got stressed as I directly dived into the group work, which started as a failure. But at the end, it was not that difficult to start programming
  • Main difficulties came with assembly language. For this part of the task, I needed to start with already made code. That is, it was difficult to start a program on my own. But understanding it was great
  • I still do not know how I could debug with ATmelStudio


  • I am most probably not going to program in assembly. But I've learnt you can add assembly into C code. Good to know, just in case!
  • Assembly code helped to start thinking again about clocks and cycles


  • This time, I programmed the small snipped of C from scratch. To see if I had understood. But I need to go through all those MACROS out there
  • ATmel studio is a good tool.
  • Again, ATtiny44a data sheet. Pretty sure I will go back to it