AVR Microcontrollers -Timers (Chapter 9 of the text book) 1 - - PowerPoint PPT Presentation

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AVR Microcontrollers -Timers (Chapter 9 of the text book) 1 - - PowerPoint PPT Presentation

Apr 30, 2023 130 likes •571 views

Microprocessors, Lecture 5: AVR Microcontrollers -Timers (Chapter 9 of the text book) 1 Contents Timers 0 and 2 of ATmega32 Timer programming in C University of Tehran 2 Timers in AVR University of Tehran 3 Timer/Counter What

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AVR Microcontrollers

  • Timers

(Chapter 9 of the text book)

1

Microprocessors, Lecture 5:

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Contents

  • Timers 0 and 2 of ATmega32
  • Timer programming in C
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Timers in AVR

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Timer/Counter

  • What is a timer?

– To count an event – To generate delay

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Timers in AVR

  • ATmega32: 3 timers

– Timer0 (8-bit) – Timer1 (16-bit) – Timer2 (8-bit)

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Timers in AVR

  • Basic registers:

– TCNTx (x=0,1,2)= timer/counter register – Keeps the timer/counter value – On reset, contains 0 – Counts up with each pulse

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Timers in AVR

  • Basic registers:

– TOVx(x=0,1,2)= timer/counter overflow flag – TOVx Becomes 1 when TCNTx overflows

» switches from 0xFF to 0x00

– Should be reset by software

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Timers in AVR

  • Basic registers:

– OCRx (x=1,2,3)= output compare register – Another way to count – The contents of OCRx are compared to TCNTx

» OCFx is set if they are equal

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Timers in AVR

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Timers in AVR

  • Basic registers:

– TCCRx (x=1,2,3)= timer/counter control register – Setting modes of operation

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TCCR0 in AVR

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TCCR0 in AVR

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TCCR0 in AVR

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Timers in AVR

  • TIFR (timer/counter interrupt flag register)
  • To keep the state of the counters
  • One register for all counter/timers
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TIFR

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Timer0 in normal mode

  • Set TCNT0 with proper value
  • Set TCCR0: which clock source? Which

prescalar? – When is set, the timer starts

  • Keep monitoring TOV0
  • Stop timer Set TCCR0
  • Clear TOV0
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Timers in AVR

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Timers in AVR

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Timers in AVR

TCCR0=0x01 //normal mode, no prescaling TCNT0=0xCE

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Timers in AVR

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Timers in AVR-CTC mode

  • Compare mode (clear timer o compare)
  • Another way to count
  • 1. Increment TCNT at each clock cycle
  • 2. OCFn=1 when OCRn=TCNTn
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Timer 2 in ATmega32

  • Just like timer 0, but no external clock

– Timer only

  • TCCR2:
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Timer programming in C

  • We can use the register names in C codes:

– TCNT0, TCNT1, TCNT2 – TIFR0,… – TCCR0,… – ….

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Timer programming in C

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Timer programming in C

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Timer 1

  • 16-bit counter/timer
  • TCNT1L and TCNT1H
  • 2 8-bit registers to control

timer 1 – TCCR1L and TCCR1H

  • 2 registers in compare

mode – OCR1A and OCR1B

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Timer 1

TCNT1 3 flags in TIFR: TOV1 and OCF1A- OCF1B

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Timer 1 control registers

  • 2 registers
  • Plenty of operation modes

TCCR1A TCCR1B

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Timer 1 control registers

TCCR1A TCCR1B

In this course, we focus on modes 0 and 4

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Timer 1 modes

  • 16 modes, we use 2 modes in this chapter:
  • Normal mode:
  • CTC mode
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Timer 1 control registers

TCCR1A TCCR1B

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Timer 1 control registers

TCCR1A TCCR1B

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Timer 1 programming

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Timer 1 programming

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Timer 1 programming

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Timer 1 programming

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Accessing 16-bit registers in AVR

  • TCNT1=0x05ff, we want to save the content of

TCNT1 in R20 and R21

  • Cannot read TCNT in one cycle

– AVR is a 8-bit machine

  • Read TCNT1L (0xff) at t0, at the same cycle occurs

TCNT=0x0600

  • Read TCNT1H (0x06)
  • The content is detected as 0x06ff instead of the correct

value 0x05ff

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Accessing 16-bit registers in AVR

  • Solution:

– AVR buffers the high byte when the lower byte is read – When the higher byte is read, the buffered value is used

  • first read the lowest byte and then the

higher byte

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Counters in AVR

  • To count external events
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Counter programming in AVR

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Counter programming in AVR

  • Configure T0 (PB0) or T1 (PB1) as input
  • Set the other registers as in timers
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Counter