Embedded Systems Design with the Atmel AVR Microcontroller Part II

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158 CHAPTER 6. TIMING SUBSYSTEM Timer/Counter Control Register A (TCCR2A) COM2A1 COM2A0 COM2B1 COM2B0 --- --- WGM21 7 Timer/Counter Control Register B (TCCR2B) FOC2A FOC2B --- --- WGM22 CS22 CS21 CS20 7 Timer/Counter Register (TCNT2) 7 Output Compare Register A (OCR2A) 7 Output Compare Register B (OCR2B) 7 Timer/Counter 2 Interrupt Mask Register (TIMSK2) --- --- --- --- --- 7 WGM20 OCIE2B OCIE2A TOIE2 Timer/Counter 2 Interrupt Flag REgister (TIFR2) --- --- --- --- --- OCF2B OCF2A TOV2 Figure 6.14: Timer 2 registers. 7 6.9 PROGRAMMING THE TIMER SYSTEM In this section, we provide several representative examples of using the timer system for various applications. We will provide examples of using the timer system to generate a prescribed delay, to generate a PWM signal, and to capture an input event. 6.9.1 PRECISION DELAY In this example,we program the ATmega164 to provide a delay of some number of 6.55 ms interrupts. The Timer 0 overflow is configured to occur every 6.55 ms. The overflow flag is used as a “clock tick” to generate a precision delay. To create the delay, the microcontroller is placed in a while loop waiting for the prescribed number of Timer 0 overflows to occur. 0 0 0 0 0 0 0
Timer/Counter Control Register B (TCCR2B) 7 Timer/Counter Control Register A (TCCR2A) 6.9. PROGRAMMING THE TIMER SYSTEM 159 CS2[2:0] Clock Source 000 None 001 clkI/0 010 clkI/0 /8 011 clkI/0 /32 100 clkI/0 /64 101 clkI/0 /128 110 clkI/0 /256 111 clkI/0 /1024 Clock Select FOC2A FOC2B --- --- WGM22 CS22 CS21 CS20 COM2A1 COM2A0 COM2B1 COM2B0 --- --- WGM21 WGM20 Mode WGM[02:00] Waveform Generation Mode Mode 0 000 Normal 1 001 PWM, Phase Correct 2 010 CTC 3 011 Fast PWM 4 100 Reserved 5 101 PWM, Phase Correct 6 110 Reserved 7 111 Fast PWM Compare Output Mode, non-PWM Mode COM2A[1:0] 00 01 10 11 COM2A[1:0] 00 01 10 11 Description Normal, OC2A disconnected Toggle OC2A on compare match Clear OC2A on compare match Set OC2A on compare match Compare Output Mode, Fast PWM Mode COM2A[1:0] 00 01 10 11 Description Normal, OC2A disconnected WGM22 = 0: normal operation, OC2A disconnected WGM22 = 1: Toggle OC2A on compare match Clear OC2A on compare match, set OC2A at Bottom (non-inverting mode) Set OC2A on compare match, clear OC2A at Bottom (inverting mode) Compare Output Mode, Phase Correct PWM Description Normal, OC2A disconnected WGM22 = 0: normal operation, OC2A disconnected WGM22 = 1: Toggle OC2A on compare match Clear OC2A on compare match, when upcounting. Set OC2A on compare match when down counting Set OC2A on compare match, when upcounting. Set OC2A on compare match when down counting Compare Output Mode, non-PWM Mode COM2B[1:0] 00 01 10 11 COM2B[1:0] 00 01 10 11 Description Normal, OC2B disconnected Toggle OC2B on compare match Clear OC2B on compare match Set OC2B on compare match Compare Output Mode, Fast PWM Mode COM2B[1:0] 00 01 10 11 Description Normal, OC2B disconnected Reserved Clear OC2B on compare match, set OC2B at Bottom (non-inverting mode) Set OC2B on compare match, clear OC2B at Bottom (inverting mode) Compare Output Mode, Phase Correct PWM Description Normal, OC2B disconnected Reserved 0 Clear OC2B on compare match, when upcounting. Set OC2B on compare match when down counting Set OC2B on compare match, when upcounting. Set OC2B on compare match when down counting Figure 6.15: Timer/Counter Control Register A and B (TCCR2A and B) bit settings.
Page 1: Embedded Systems Design with the At
Page 4 and 5: iv An Introduction to Logic Circuit
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Page 8 and 9: ABSTRACT This textbook provides pra
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270 APPENDIX A. ATMEGA164 REGISTER
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272 APPENDIX A. ATMEGA164 REGISTER
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Author’s Biography STEVEN F. BARR
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296 INDEX switch debouncing, 187 sw
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Embedded Systems Design with the Atmel AVR Microcontroller Part II

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