L15 timers-counters-in-atmega328 p
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The document discusses timers and counters in the Atmega328 microcontroller. It describes the three timers: Timer/Counter0 is 8-bit, Timer/Counter1 is 16-bit, and Timer/Counter2 is 8-bit. Timers can be used for time delays, event counting, or PWM signal generation. Timer/Counter1 has additional features like 16-bit PWM and input capture. Modes like normal mode and CTC mode are described for Timer/Counter1. Example C code is provided to set up Timer1 for delays and interrupts. Calculations for delays using Timer1 in different modes are also demonstrated.
L15 timers-counters-in-atmega328 p
- 1. Timers/Counters in Atmega328 (Lecture-15) R S Ananda Murthy Associate Professor Department of Electrical & Electronics Engineering, Sri Jayachamarajendra College of Engineering, Mysore 570 006 R S Ananda Murthy Timers/Counters in Atmega328
- 2. Timer/Counters in Atmega328P Timer/Counter0 – 8 bit. Timer/Counter1 – 16 bit. Timer/Counter2 – 8 bit. Timer/Counter can be used to cause time delay, to count events, or to generate PWM signal. R S Ananda Murthy Timers/Counters in Atmega328
- 3. General Features of Timer/Counter Counter/Timer Register Oscillator External Source Counter/Timer Flag Interrupt Prescaler Clk External Source is fed as Clk input to Timer/Counter Register when used as counter. Oscillator is fed as Clk input to Timer/Counter Register when used as timer. Prescaler divides the oscillator frequency by a specific constant. When Timer/Counter register reaches a specific value,a flag will be set and optionally an interrupt can be issued. R S Ananda Murthy Timers/Counters in Atmega328
- 4. Features of 16-bit Timer/Counter1 with PWM Permits 16-bit PWM Two independent Output Compare Units Double Buffered Output Compare Registers One Input Capture Unit Input Capture Noise Canceler Clear Timer on Capture Match (Auto Reload) Glitch-free, Phase Correct Pulse Width Modulator Variable PWM period Frequency Generator External Event Counter Four independent interrupt sources (TOV1, OCF1A, OCF1B, ICF1) R S Ananda Murthy Timers/Counters in Atmega328
- 5. Timer/Counter1 Block Diagram R S Ananda Murthy Timers/Counters in Atmega328
- 6. Registers Pertaining to Timer/Counter1 Timer/Counter1 High and Low bytes Output Compare Register1A High and Low Bytes Output Compare Register1B High and Low Bytes R S Ananda Murthy Timers/Counters in Atmega328
- 7. Registers Pertaining to Timer/Counter1 Timer/Counter Control Register1A Timer/Counter Control Register1B Timer/Counter Control Register1C R S Ananda Murthy Timers/Counters in Atmega328
- 8. Registers Pertaining to Timer/Counter1 Timer/Counter1 Interrupt Mask Register Timer/Counter1 Interrupt Flag Register1 By setting appropriate bits in TIMSK1 the corresponding interrupt can be enabled. When ISR is executed corresponding to a timer/counter1 event, the corresponding flag is cleared in the TIFR1. By setting appropriate bits in TIFR1 the corresponding flag can be cleared. R S Ananda Murthy Timers/Counters in Atmega328
- 9. Timer/Counter1 Mode 0 and Mode 4 Interrupt Vectors ISR Name to be used in C Source of Interrupt TIMER1_CAPT_vect Timer/Counter1 Capture Event TIMER1_COMPA_vect Timer/Counter1 Compare Match A TIMER1_COMPB_vect Timer/Counter1 Compare Match B TIMER1_OVF_vect Timer/Counter1 Overflow R S Ananda Murthy Timers/Counters in Atmega328
- 10. Modes of Operation of Timer/Counter1 Normal Mode (also known as Mode 0) Clear Timer on Compare (CTC) Match Mode (also known as Mode 4 and Mode 12) In Mode 4 comparison is done with OCR1A. In Mode 12 comparison is done with ICR1. Fast PWM Mode Phase Correct PWM Mode Phase and Frequency Correct PWM Mode The last three modes are PWM modes. Here we discuss only Normal Mode and CTC mode. Mode selection can be made by setting appropriate bits in TCCR1A and TCCR1B registers. R S Ananda Murthy Timers/Counters in Atmega328
- 11. Setting Timer/Counter1 Clock Source and Prescaler CS12 CS11 CS10 Effect 0 0 0 No clock (Timer/Counter stops) 0 0 1 clk (no prescaling) 0 1 0 clk/8 0 1 1 clk/64 1 0 0 clk/256 1 0 1 clk/1024 1 1 0 Ext. clk on T1 pin, falling edge 1 1 1 Ext. clk on T1 pin, rising edge CS12, CS11 and CS10 bits are in TCCR1B register. Timer/Counter1 is inactive when no clock source is selected. Timer/Counter1 starts when clock source is set. R S Ananda Murthy Timers/Counters in Atmega328
- 12. Normal Mode (Mode 0) This mode can be selected by making WGM13 = 0, WGM12 = 0 in TCCR1B and WGM11 = 0, WGM10 = 0 in TCCR1A. In this mode there is no comparison with either ICR1 or OCR1A. In this mode the timer counts up for every clock cycle until it reaches $FFFF (also referred to as MAX) and then resets to $0000 in the next clock cycle. When the timer value changes from $FFFF to $0000, the TOV1 flag is set. An interrupt can be generated when TOV1 flag is set by setting TOIE1 bit in TIMSK1. R S Ananda Murthy Timers/Counters in Atmega328
- 13. CTC Mode (Mode 4) This mode can be selected by making WGM13 = 0, WGM12 = 1 in TCCR1B and WGM11 = 0, WGM10 = 0 in TCCR1A. In this mode the timer counts up until it reaches the value stored in OCR1A (also referred to as TOP) and then resets from TOP to $0000. When the timer resets from TOP to $0000, the OCF1A flag will be set. An interrupt can be generated when OCF1A flag is set by setting OCIE1A bit in TIMSK1. R S Ananda Murthy Timers/Counters in Atmega328
- 14. Example C Statements to Set Up Timer1 R S Ananda Murthy Timers/Counters in Atmega328
- 15. Maximum Delay using Timer 1 in Mode 0 Calculate maximum time delay that can be realized using Timer 1 in Mode 0 with prescaler value of 1024. Assume that MCU clock frequency is 16 MHz. Frequency of clock signal applied to Timer 1 is given by fclk = 16×106 1024 = 15625 Hz Therefore maximum delay possible is tdelay(max) = 65536 15625 = 4.1943 s R S Ananda Murthy Timers/Counters in Atmega328
- 16. Timer1 Initial Count in Mode 0 for a Given Delay Assuming MCU clock frequency to be 16 MHz and prescaler value of 1024, find the initial number N to be loaded in TCNT1H and TCNT1L to get a time delay close to 1 second in Mode 0. No. of steps required to cause a delay of 1 s is given by n = 15625×1 = 15625 = 65535−N +1 Therefore N = (49911)10 = 0xC2F7 So, TCNT1H = C2 and TCNT2L = F7. R S Ananda Murthy Timers/Counters in Atmega328
- 17. Using Timer1 to cause Delay Write C code to setup Timer1 (16-bit timer) of Atmega328P MCU to give a 1 s time delay assuming that the MCU is operating at 16 MHz clock with prescaler set to 1024. Use timer interrupt to blink an LED connected to an output port line. Show timer calculations and hardware connections clearly. The number to be loaded in Output Compare Register1 (OCR1) is given by OCR1 = 16×106 1024 ×1 −1 = (15624)10 = (3D08)16 R S Ananda Murthy Timers/Counters in Atmega328
- 18. Timer/Counter1 Program Using Interrupt R S Ananda Murthy Timers/Counters in Atmega328
- 19. Using Timer0 as Counter Assuming that a 1 Hz clock pulse is fed into pin T0 of Atmega328P MCU, write C code to use the TOV0 flag to extend Timer0 to a 16-bit counter and display the counter on PORTC and PORTD. R S Ananda Murthy Timers/Counters in Atmega328
- 20. License This work is licensed under a Creative Commons Attribution 4.0 International License. R S Ananda Murthy Timers/Counters in Atmega328