Timers and Low Power Modes

1. Timers and Low Power Modes Presented by IEEE of Texas A&M

2. About This Workshop • Based on the MSP430G2553 microcontroller by Texas Instruments • Powerpoint and code available at ieeetamu.org/mcc/timersLPM • Workshop Reference available at ieeetamu.org/mcc/wsref • Footnotes refer to User Guide (UG), Datasheet, or Workshop Reference (WSRef)

3. Import code projects into Code Composer • Follow instructions in the Workshop Reference or at ieeetamu.org/mcc/importing • Code: ieeetamu.org/mcc/timersLPM • Projects to import: • Longest 16 Bit Timer • 32 Bit Timer • PWM

4. Extremely Useful Documents • User's Guide – MSP430x2xx Family • http://www.ti.com/lit/ug/slau144i/slau144i.pdf • All general MSP430 information • Ex: MSP430 Architecture, Instruction Set, Registers, clocks, timers, module types and functionality • MSP430G2x53 Datasheet • http://www.ti.com/lit/ds/slas735g/slas735g.pdf • Information specific to individual set of chips • Ex: List of included modules, pin-outs, memory size

5. Topics • Introduction to Timers • 16 Bit Timers • 32 Bit Timers • Low Power Modes • Pulse Width Modulation

6. Introduction To Timers

7. Timers • Timers keep count of things • They can be used to plan out tasks • Ex. Count to 30, then execute a task. • Simple right? not exactly. • We are limited to 16 bit timers • 16 bit - only counts up to 216 • Can emulate a 32+ bit timer using software • 32 bit - only count up to 232

8. Types of Timers • Continuous Timers • Counting up Timers • Up-Down Timers • All types are available for Timer A0 and A1 • All can be used as a real time timer

9. Continuous Timers • Counts up to the max value (0xFFFF, 65535) every time • Max value is always 0xFFFF

10. Counting Up Timer • Counts up to a certain value (TACCR0) then repeats • Almost identical to a continuous timer • Always increasing or “counting up”

11. Up – Down Timers • Counts up to a value (TACCR0) and then counts down back to zero • Goes both up and down

12. 16 And 32 Bit Timers

13. MSP430 Clock Module

14. MSP430 Clock Sources for Timers • MCLK – Master Clock • Can’t be used as source • Used by the CPU and system • SMCLK – Sub-System Master clock • ACLK – Auxiliary clock • DCO – Digitally controlled oscillator • Can’t be used as source

15. Timer/Clock Resolution • We can trigger an interrupt at a certain time • We can use the 16 bit timer or increase the maximum value using a variable to emulate a 32 bit timer • We can use the 32 bit when the 16 bit doesn’t suffice

16. TACTL - Timer A Control Register • CCR0 - The capture compare register compare its value with the timer. Divider for the input clock Timer Modes Clock Source Select Section 12.3.1 in the MSP430x2xx user guide (Page 378)

17. TACTL - Timer A Control Register • Timer A (TACTL) • Consists of • The Timer A clock source (TASSELx) • These bits select the divider for the input clock (IDx) • Clock mode control (MCx) Section 12.3.1 in the MSP430x2xx user guide (Page 378)

18. TACTL - Timer A Control Register • The Timer A clock source (TASSELx) • TACLK (TASSEL_0) • ACLK (TASSEL_1) • SMCLK (TASSEL_2) • INCLK (TASSEL_3) Section 12.3.1 in the MSP430x2xx user guide (Page 378)

19. TACTL - Timer A Control Register • These bits select the divider for the input clock (IDx) • (ID_0) is divide by 1 • (ID_1) is divide by 2 • (ID_2) is divide by 4 • (ID_3) is divide by 8 Section 12.3.1 in the MSP430x2xx user guide (Page 378)

20. TACTL - Timer A Control Register • Clock mode control (MC_1) • (MC_0) Stop mode: the timer halts • (MC_1) Up mode: the timer counts up CCR0 • (MC_2) Continuous mode: the timer counts up to the max value of CCR0 • (MC_3) Up down mode: the timer counts up CCR0 and then down to 0x0000h Section 12.3.1 in the MSP430x2xx user guide (Page 378)

21. 16 Bit Timer Code • Now open the project for 16 bit timer • Then run the code void main(void) { WDTCTL = WDTPW + WDTHOLD; // Stop WDT P1DIR |= GREEN_LED + RED_LED; // P1.0 output CCTL0 = CCIE; // CCR0 interrupt enabled CCR0 = 0xFFFF; // max value for 16 bit timer TACTL = TASSEL_2 + MC_1 + ID_3; _BIS_SR(LPM0_bits + GIE); // Enter LPM0 w/interrupt } #pragmavector=TIMER0_A0_VECTOR __interruptvoidTimer_A (void) { P1OUT ^= RED_LED; // Toggle P1.0 }

22. Exercise: 16 Bit Timer Code 1. Change the hex value for CCTL0 2. Change the ID value 3. Change the timer mode or timer select voidmain(void) { WDTCTL = WDTPW + WDTHOLD; // Stop WDT P1DIR |= (GREEN_LED + RED_LED); // P1.0 output CCTL0 = CCIE; // CCR0 interrupt enabled CCR0 = 0xFFFF; TACTL = TASSEL_2+ MC_1+ ID_3; _BIS_SR(LPM0_bits + GIE); // Enter LPM0 w/interrupt } #pragmavector=TIMER0_A0_VECTOR __interruptvoidTimer_A (void) { P1OUT ^= RED_LED; // Toggle P1.0 }

23. 32 Bit Timer Code • Now open the project for 32 bit timer and close the 16 bit timer. • Then run the code unsignedint timer_32_flag = 0; void main(void) { WDTCTL = WDTPW + WDTHOLD; // Stop WDT P1DIR |= (GREEN_LED + RED_LED); // Green and Red led output CCTL0 = CCIE; // CCR0 interrupt enabled CCR0 = 0xFFFF; // value that the timer counts up to TACTL = TASSEL_2 + MC_1 + ID_3 _BIS_SR(LPM0_bits + GIE); // Enter LPM0 w/ interrupt. } #pragmavector=TIMER0_A0_VECTOR // Timer A0 interrupt service routine __interruptvoidTimer_A (void) { timer_32_flag++; // counts the number of times that we have reached the 16 bit timer if(timer_32_flag > 3) { P1OUT ^= RED_LED; // Toggle the Red LED timer_32_flag = 0; // Reset the flag } }

24. Exercise: 32 Bit Timer 1. Now change the CCR0 value 2. Change the ID_3 to another IDx value 3. Change the timer mode or timer select voidmain(void) { WDTCTL = WDTPW + WDTHOLD; P1DIR |= (GREEN_LED + RED_LED); CCTL0 = CCIE; CCR0 = 0xFFFF; TACTL = TASSEL_2+ MC_1+ ID_3; _BIS_SR(LPM0_bits + GIE); }

25. Exercise: 32 Bit Timer 4. Change the value the flag can go up to #pragmavector=TIMER0_A0_VECTOR __interruptvoidTimer_A (void) { //counts times interrupt has triggered timer_32_flag++; if(timer_32_flag > 3) { P1OUT ^=RED_LED; // Toggle the Red LED timer_32_flag = 0; } }

26. Low Power Modes

27. Low Power Modes • Allows you to scale power usage of the microcontroller • Why? You can shut off parts of the MSP430 that you aren’t using.

28. 6Types of Low Power Modes • AM – All clocks are active • LPM0 - The CPU is disabled and MCLK is disabled. • LPM1 - The DCO’s generator is disabled. • LPM2 – SMCLK is also disabled. • LPM3 – Same as LPM2. Don’t know why this was added. • LPM4 – The ACLK and the crystal oscillator are also disabled. • NOTE: As Low Power mode rises, all previous low power modes are also included • (Ex. LPM3 includes LPM0-LPM2)

29. Exercise: Sleep Mode on 32 bit Timer • LPM0_bits turns off the CPU • GIE allows general interrupts • What happens in our code when the low power mode changes? voidmain(void) { WDTCTL = WDTPW + WDTHOLD; P1DIR |= (GREEN_LED + RED_LED); CCTL0 = CCIE; CCR0 = 0xFFFF; TACTL = TASSEL_2 + MC_1 + ID_3; _BIS_SR(LPM0_bits + GIE); }

30. PWM (Pulse Width Modulation)

31. PWM • Controls the percentage of time the wave is high across one period • The device will see the average voltage • Ex. If the duty cycle is less, an LED will look dimmer • Ex. A motor at certain speeds Average Voltage

32. PWM: Duty Cycles CCR0 CCR1 Timer ON OFF PWM Signal

33. PWM: Duty Cycles CCR0 CCR1 Timer ON OFF PWM Signal

34. PWM Code • Now open the project for PWM and close the 32 bit timer. • Then run the code voidmain(void) { WDTCTL = WDTPW + WDTHOLD; // Stop WDT P1DIR |= GREEN_LED; // P1.6 output P1SEL |= GREEN_LED; // P1.6 TA0.1 options CCR0 = 0xFFFF-2; // PWM Period CCTL1 = OUTMOD_7; // CCR1 reset/set CCR1 = 0x8000; // CCR1 PWM duty cycle TACTL = TASSEL_2 + MC_1; // SMCLK, up mode _BIS_SR(LPM0_bits); // Enter LPM0 }

35. PWM Code: Out Modes • Out Modes • OUTMOD_0 • OUTMOD_1 • OUTMOD_2 • OUTMOD_3: The output is set when the timer counts to the TACCRx value. It is reset when the timer counts to the TACCR0 value • OUTMOD_4 • OUTMOD_5 • OUTMOD_6 • OUTMOD_7: The output is reset when the timer counts to the TACCRx value. It is set when the timer counts to the TACCR0 value. • Only worry about OUTMOD_3 and OUTMOD_7

36. Exercise: PWM Code • Change the PWM duty cycle • Change the OUTMOD voidmain(void) { WDTCTL = WDTPW + WDTHOLD; // Stop WDT P1DIR |= GREEN_LED; // P1.6 output P1SEL |= GREEN_LED; // P1.6 TA0.1 options CCR0 = 0xFFFF; // PWM Period CCTL1 = OUTMOD_7; // CCR1 reset/set CCR1 = 0x8000; // CCR1 PWM duty cycle TACTL = TASSEL_2 + MC_1; // SMCLK, up mode _BIS_SR(LPM0_bits); // Enter LPM0 }