ECTE333: Digital Hardware 2 7 L10: Pulse Width Modulator .

External interrupts: ext int.cExternal interrupts: Testing ext int.c#include avr/io.h Writea C theinterrupt-drivenprogramto toggle port B whenever a switchTo testexternal interruptexample:on the STK500 board is pressed. The program should use an external Connect INT1 pin (pin D.3) to switch SW7 on STK500 board.interrupt. Connect GRD pin of Port D to GRD pin of SW connector.#include avr/interrupt.h ISR(INT1 vect){PORTB ( PORTB);// handler for INT1 interrupt// toggle port B Connect Port B to LED connector.} Compile, download program.int main(void) { Press switch SW7.GICR (1 INT1); // enable interrupt INT1MCUCR (1 ISC10); // triggered on any change to INT1 pin (D.3)sei();// enable interrupt subsystem globallyDDRB 0xFF;// set port B for outputVideo demo link: [avr]/ecte333/ext int.mp4PORTB 0b10101010; // initial valuewhile (1) {;}// infinite loopreturn 0;}Lam Phung University of Wollongong, 2010.259.2 Timers in ATmega16Lam Phung University of Wollongong, 2010.26Timer terminologyMany computer applications require accurate timing.Input Capture: An input signal is connected to a pin, designated as input capturepin, of the timer.Examples include When a preset event (rising edge, falling edge, change) occurs onthe input capture pin, the current value of the timer is stored in aregister. recording the time when an event occurs, calculating the time difference between events, performing tasks at specific or periodic time instants, creating accurate time delays,Output Compare: generating waveforms of certain shape, period or duty cycle. A timer usually has a pin designated as output compare pin. When the timer reaches a preset value, the output compare pin canbe automatically changed to logic 0 or logic 1.Lecture 9 and Lecture 10 focus on the use of timers to perform theabove time-related processing.Lam Phung University of Wollongong, 2010.27Lam Phung University of Wollongong, 2010.28

Overview of Timers in ATmega16Overview of Timers in ATmega16When the internal system clock is used, a prescaler can be used makeATmega16 has three timers: Timer 0, Timer 1 and Timer 2.the timer count at a slower rate.Each timer is associated with a counter and a clock signal.Example:The counter is incremented by 1 in every period of the timer’s clocksignal. Suppose the system clock rate 1Mhz (1μs per cycle). Suppose a timer prescaler of 64 is used.The clock signal of a timer can come from Then, timer will increment every 64μs. the internal system clock or an external clock source.29 University of Wollongong, 2010.Lam PhungOverview of Timers in ATmega16Timer 0OverallLam Phung University of Wollongong, 2010.30Study planTimer 1Timer 2In Lecture 9, we focus on- 8-bit counter- 16-bit counter- 8-bit counter- 10-bit prescaler- 10-bit prescaler- 10-bit prescaler- PWM- PWM- PWM- Frequency generation- Frequency generation- Frequency generation- Event counter- Event counter- Event counter measuring time, creating time delay,- Output compare- Output compare: 2- Output compare measuring period/duty cycle of a signal, operations of Timer 1, using Timer 1 overflow interrupt,Functions using Timer 1 input capture interrupt,channels information required for Lab 9.- Input captureOperationmodes- Normal mode- Normal mode- Normal mode- Clear timer on- Clear timer on- Clear timer oncompare matchcompare matchIn Lecture 10, we will learn using Timer 1 output compare interrupt,compare match- Fast PWM- Fast PWM- Fast PWM- Phase correct PWM- Phase correct PWM- Phase correct PWM generating PWM signals, information required for Lab 10.Timer 1 has the most capability among the three timers.Lam Phung University of Wollongong, 2010.31Lam Phung University of Wollongong, 2010.32

Timer 1: An overviewTimer 1: Block diagram16-bit counter.External clockpinCurrent timer/counter value10-bit prescaler: 8, 64, 256, 1024Output Comparepinscan trigger a timer overflow interrupt when counter reaches MAX.Output CompareRegisterscan trigger an input capture interrupt when an event occurs on theinput capture pin. timer value is stored automatically in a register. input capture pin for Timer 1 is ICP1 (D.6).Input Capture registercan trigger an output compare match interrupt when timer reaches apreset value.Input Capture pinTimer/CounterControl Registers There are two independent output compare channels A and B.Not shown here: TIMSK and TIFR registersLam Phung University of Wollongong, 2010.33Timer 1 Relevant pinsLam Phung University of Wollongong, 2010.34Timer 1 Five groups of registers1) Timer/Counter 1 TCNT1 16-bit register that stores the current value of the timer.2) Timer/Counter 1 Control Registers TCCR1A and TCCR1B To configure the operations of Timer 1.3) Input Capture Register ICR1 to store timer value when an event occurs on input capture pin.4) Interrupt registers TIMSK to enable timer interrupts TIFR to monitor status of timer interrupts.5) Output Compare Registers OCR1A, OCR1B To store the preset values for output compare.used in thislectureLam Phung University of Wollongong, 2010.35Lam Phung University of Wollongong, 2010.36

Timer 1 Five groups of registers9.2.1 Timer/Counter 1 Control Register A (TCCR1A)76543210COM1A1 COM1A0 COM1B1 COM1B0 FOC1A FOC1B WGM11 WGM10Specify Waveform Generation Modeused with WGM13, WGM12WGM13.WGM10 0000 for normal mode.1 to force output compare on channel B1 to force output compare on channel AOutput compare mode for channel BOutput compare mode for channel A University of Wollongong, 2010.Lam Phung379.2.2 Timer/Counter 1 Control Register B (TCCR1B)765ICNC1ICES1-43WGM13 WGM12210CS12CS11CS10Lam Phung University of Wollongong, 2010.38Clock selectclock select (next slide)select Waveform Generation Mode, used with WGM11, WGM10WGM13.WGM10 0000 for normal mode.input capture edge select: 1 will select rising edge, 0 will select falling edgeFor ATmega16, the internal clock is set by default at clkI/O 1MHz.Timer 1 can run using the internal or external clock.1 to activate input capture noise cancellerIf using the internal clock, we can set Timer 1 to run at a speed that is8, 64, 256 or 1024 times slower than the internal clock.Lam Phung University of Wollongong, 2010.39Lam Phung University of Wollongong, 2010.40

9.2.3 Timer/Counter Interrupt Mask Register (TIMSK)76OCIE2TOIE25432TICIE1 OCIE1A OCIE1B TOIE110OCIE0TOIE09.2.4 Timer/Counter Interrupt Flag Register (TIFR)765OCF2TOV2ICF143OCF1A OCF1B210TOV1OCF0TOV0For Timer 0For Timer 0Timer 1 Overflow Interrupt EnableTimer 1 Overflow Interrupt Flag: set to 1 when overflowTimer 1 Output Compare B Match Interrupt Enable: 1 to enableTimer 1 Output Compare B Match Flag: set to 1 when matchTimer 1 Output Compare A Match Flag: set to 1 when matchTimer 1 Output Compare A Match Interrupt Enable: 1 to enableTimer 1 Input Capture Flag: set to 1 when capture event occursTimer 1 Input Capture Interrupt Enable: 1 to enableFor Timer 2For Timer 2This register has flags that indicate when a timer interrupt occurs. University of Wollongong, 2010.Lam Phung419.3 Timer applicationsLam Phung University of Wollongong, 2010.429.3.1 Creating an accurate delayWrite a C program for ATmega16 to toggle PORTB every 2 seconds.In this section, we consider three applications of Timer 1.It should use timer 1 overflow interrupt to create delays of 2s each.9.3.1 Creating an accurate delay using timer overflow interrupt.Analysis Internal system clock: 1MHz. With no prescaler, Timer 1 will increment every 1 μs.9.3.2 Measuring elapsed time between two events. Because Timer 1 is 16-bit counter, it will overflow every 216 μs. To have a 2s delay, we need Timer 1 to overflow for 2s/216 μs 31times.9.3.3 Measuring the period of a square signal using input captureinterrupt.Coding Write code to enable & intercept Timer 1 overflow interrupt. Use interrupt handler to count the number of overflows. When number of overflows 31, toggle port B.Lam Phung University of Wollongong, 2010.43Lam Phung University of Wollongong, 2010.44

Creating an accurate delay: timer delay.c9.3.2 Measuring elapsed time#include avr/io.h #include avr/interrupt.h To measure a time interval using Timer 1, we must keep track of bothvolatile int overflow count; the number of times that Timer 1 has overflowed: nISR(TIMER1 OVF vect){// handler for Timer1 overflow interruptoverflow count ;// increment overflow countif (overflow count 31){ // when 2s has passedoverflow count 0;// start new countPORTB PORTB;// toggle port B}} the current counter value:If we reset n and TCNT1 at the beginning of the interval, then thetime elapse is (assuming no prescaler, 1MHz clock)t n x 65536 TCNT1 (μs)int main(void) {DDRB 0xFF;// set port B for outputPORTB 0x00;// initial value of PORTBoverflow count 0; // initialise overflow countTCCR1A 0b00000000; // normal modeTCCR1B 0b00000001; // no prescaler, internal clockTimer OverflowsTCNT1n 0TCNT1 0TIMSK 0b00000100; // enable Timer 1 overflow interruptsei();// enable interrupt subsystem globallywhile (1){;}return 0;TCNT112ntime interval t// infinite loopstart at time t1stop at time t2}Lam Phung University of Wollongong, 2010.45Measuring elapsed timeLam Phung University of Wollongong, 2010.46Measuring elapsed time: measure time.c#include avr/io.h #include avr/interrupt.h #include inttypes.h Use Timer 1 to measure the execution time of some custom C code.volatile uint32 t n;ISR(TIMER1 OVF vect){// handler for Timer1 overflow interruptn ;// increment overflow count}int main(void) {int i, j;uint32 t elapse time;Approach: Clear Timer 1 when the code starts. Record Timer 1 when the code finishes.TCCR1A 0b00000000; // normal modeTCCR1B 0b00000001; // no prescaler, internal clockTIMSK 0b00000100; // enable Timer 1 overflow interrupt Also, use Timer 1 Overflow Interrupt to keep track of how manytimes it has overflowed.n 0;// reset nTCNT1 0;// reset Timer 1sei();// enable interrupt subsystem globally// ----- start code -------------for (i 0; i 100; i )for (j 0; j 1000; j ){;}// ----- end code ----------------elapse time n * 65536 (uint32 t) TCNT1;cli();// disable interrupt subsystem globallyreturn 0;}Lam Phung University of Wollongong, 2010.47Lam Phung University of Wollongong, 2010.48

9.3.3 Measuring period of a square signalMeasuring period of a square signalAssumption: the input signal has a high frequency, hence timeroverflow can be ignored.Use Timer 1 input capture interrupt to measure the period of a squaresignal.Analysis:Implementation: The period of a square wave the time difference betweentwo consecutive rising edges. Select timer operations: normal, no prescaler, internal clock 1MHz,noise canceller enabled, input capture for rising edges. Connect the square wave to input capture pin of Timer 1.TCCR1A 0b00000000; Configure input capture module to trigger on a rising edge.TCCR1B 0b00000001;Input capture interrupt is triggered.Read ICR1 register.Input capture interrupt is triggered.Read ICR1 register again.periodLam Phung Enable input capture interrupt:TIMSK 0b00100000;square waveform University of Wollongong, 2010.49measure period.c University of Wollongong, 2010.50Testing measure period.c#include avr/io.h #include avr/interrupt.h #include inttypes.h Writea C theinterrupt-drivenprogramto toggle port B whenever a switchTo testcode for measuringperiod:on the STK500 board is pressed. The program should use an external Connect Input Capture pin (D.6) to square wave generator oninterrupt.WishMaker.uint16 t period;ISR(TIMER1 CAPT vect){period ICR1;TCNT1 0;PORTB (period }Lam Phung// handler for Timer1 input capture interrupt// period value of Timer 1 stored in ICR1// reset Timer 18); // display top 8-bit of period on PORT B Connect GRD pin of Port D to GRD pin of WishMaker. Connect Port B to LED connector. Compile, download program.int main(void) {DDRB 0xFF; Change frequency of square ware and observe output on LEDs.// set port B for outputTCCR1A 0b00000000;TCCR1B 0b11000001;TIMSK 0b00100000;sei();while (1){;}return 0;//////////normal modeno prescaler, rising edge, noise cancellerenable Timer 1 input capture interruptenable interrupt subsystem globallyinfinite loopVideo demo link: [avr]/ecte333/measure period.mp4}Lam Phung University of Wollongong, 2010.51Lam Phung University of Wollongong, 2010.52

Extending measure period.cSummaryWhat we learnt in this lecture:The code given here assumes that there is no timer overflow betweentwo rising edges of the square signal. How to write an interrupt-driven program in C for ATmega16. Programming serial and external interrupts in C. Overview of timers in ATmega16.In Lab 9, you are required to extend the code so that a correct period ismeasured for low-frequency signals. Using Timer1 overflow and input capture interrupts in 3 applications.What are next activities? Tutorial 9: ‘Timers’.It is necessary to intercept timer overflow (as in Examples 9.3.1 and9.3.2). Lab 9: ‘Timers’ Complete the online Pre-lab Quiz for Lab 9.The measure period should also be sent through the serial port to PCfor testing.Lam Phung University of Wollongong, 2010.53 Write programs for Tasks 1 and 2 of Lab 9. See video demos of Lab 9: [avr]/ecte333/lab09 task1.mp4[avr]/ecte333/lab09 task2.mp4Lam Phung University of Wollongong, 2010.54

Later, we’ll study steps for interrupt programming in C, via 2 examples. 9.1.1 USART RXD Complete interrupt 9.1.2 External interrupts 1. Include header file avr\interrupt.h . 2. Use C macro ISR() to declare the interrupt handler and update IVT. 3. Enable the specific interrupt. 4. Configure details abo