PIC16 Timer Programming in Hitech-C

1. EET203Microcontroller Systems DesignPIC16 Timer Programming in Hitech-C

2. Today’s Lecture • List the Timers of PIC16 and their associated registers • Describe the various modes of the PIC16 timers • Program the PIC16 timers in ‘Hitech C’ to generate time delays • Program the PIC16 timers in ‘Hitech C’ • As event counters

3. Introduction • PIC16 has one(1) to three(3) timers • Depending on the family number/models. • Ex: PIC16F877A have three(3) timers; Timer0, Timer1 and Timer2. • These timers can be used as • Timers to generate a time delay. • Counters to count events happening outside the C.

4. Programming timers 0 and 1 • A register whose value is continually increasing to 255, and then it starts all over again: 0, 1, 2, 3, 4...255....0,1, 2, 3......etc. • Every timer needs a clock pulse to tick. • Clock source can be • Internal 1/4th of the frequency of the crystal oscillator on OSC1 and OSC2 pins (Fosc/4) is fed into timer • External: pulses are fed through one of the PIC18’s pins  Counter

5. Timer0 registers and programming • All instructions are written to the TMR0 register. • Consist of a register called ‘OPTION_REG’ Register, which is 8 bits of size. • Readable and writable register which contains various control bits to configure the TMR0.

6. Timer0 registers and programming

7. T0CS(Timer0 clock source) • This bit used to decide whether the clock source is internal or external. • If T0CS=0Then Fosc/4 is used as clock source, used for delay generation. • If T0CS=1the clock source is external and comes from an external source, used as event counter.

8. Timer clock source External Source Internal Source 8

9. Timer0 registers and programming • Example • If OPTION_REG=0b00110000; • External clock • High-to-low transition • Timer0 module • Prescale 1:2

10. Timer0 registers and programming • Typical calculations for creating an 18ms interrupt repeat rate using PIC Timer0 (Prescaler ratio of 1:128 and 4Mhz internal clock input). • Fosc/4 or 4MHz/4 =1MHz • Period input to Timer0 which is:1/(1MHz/128) = 128s • 128s is counted by Timer 0 and it will overflow after 141 counts (or 18ms) • 18ms /128s  141counts • Overflowtime=4 x Toscx Prescaler x (256-TMR0)

11. TMR0IF flag bit • TMR0IF is (Timer0 interrupt flag) is a part of the INTCON (interrupt control) register. • When the timer reaches its maximum value of FFH, it rolls over to 00, and TMR0IF is set to 1. INTCON (Interrupt Control Register) has the TMR0IF Flag

12. Programming in 8-bit mode • Load the value into the OPTION_REG register. • Load reg. TMR0 with initial value. • Start the timer with instruction OPTION_REG=0b00000011; //Timer0 on • Keep monitoring the timer flag (TMR0IF) to see if it is raised. • Stop the timer. • Clear the TMR0IF flag. INTCON=0b00000000; //Clear interrupt flag • Go Back to step 2.

13. Example1 Write a program to generate a square wave of 50% duty cycle on pin PORTB.5. Use Timer0 with prescaler 16 (use 10MHz clock). With overflow is 1.152 x10-4 s.

14. Example1: Program #include <htc.h> __CONFIG (FOSC_HS & WDTE_OFF & PWRTE_OFF & BOREN_OFF & LVP_OFF); #define _XTAL_FREQ 10000000 #define LED5 RB5 void pic_init(void); void timer_init(void); main() { pic_init(); //initialize PIC timer_init(); //initialize Timer Module while(1) { OPTION_REG=0b00000011; //start Timer1 if(INTCON==0b00000100) { OPTION_REG=0b00100011; //off Timer1 LED5 = !LED5; INTCON=0b00000000; TMR0=0xEE; }

15. Example1: Program } } void pic_init(void) { TRISB=0b00000000; PORTB=0b00000000; } void timer_init(void) { OPTION_REG=0b00100011; TMR0=0xEE; }

16. Example 1: Circuit Layout

17. Example1: Simulation Result

18. 1 2 17 18 EE FE 0F EF FF 00 TMR0IF=0 TMR0IF=0 TMR0IF=0 TMR0IF=0 TMR0IF=0 TMR0IF=1 Example 1: Analysis • Timer1 counts up from EE, FE, ….,FFH. • From FFH to 00H, TMR0IF is set to 1. • T = 4/10MHz = 0.4s (Each tick consume 0.4s). • How many tick? (FF-EE) + 1 = 18 Decimal ticks. • Time delay = 18 x 0.4s = 7.2s for half the pulse

19. T1CON (Timer1 control) register 19

20. T1CON (Timer1 control) register • Each timer has a control register called TxCON, to set various timer operation modes. • T1CON is 8-bit register used to control Timer1. • Example • If T1CON= 0b00000010; • 16-bit • No prescaler • Rising edge

21. Characteristics and operations of 16-bit mode • 16-bit timer, 0000 to FFFFH. • After loading TMR1H and TMR1L, the timer must be started. • Count up, till it reaches FFFFH, then it rolls over to 0000 and activate TMR1IF bit. • Then TMR1H and TMR1L must be reloaded with the original value and deactivate TMR1IF bit.

22. Characteristics and operations of 16-bit mode

23. Programming in 16-bit mode • Load the value into the T1CON register. • Load reg. TMR1H followed by reg. TMR1L with initial value. • Start the timer with instruction T1CON=0b00000001; //Timer1 on • Keep monitoring the timer flag (TMR1IF) to see if it is raised. • Stop the timer. • Clear the TMR1IF flag. PIR1=0b00000000; //Clear interrupt flag • Go Back to step 2.

24. Example 2: Program • Write a program to generate a square wave of 50% duty cycle on pin PORTB.5. Use Timer1 without prescaler (use 10MHz clock). The overflow is 5.6 us. #include <htc.h> __CONFIG (FOSC_HS & WDTE_OFF & PWRTE_OFF & BOREN_OFF & LVP_OFF); #define _XTAL_FREQ 10000000 #define LED5 RB5 void pic_init(void); void timer_init(void); main() { pic_init(); //initialize PIC timer_init(); //initialize Timer Module while(1) { T1CON=0b00000001; //start Timer1

25. Example 2: Program if(PIR1==0b00000001) { T1CON=0b00000000; //off Timer1 LED5 = !LED5; //Toggle portb bit 5 PIR1=0b00000000; //Clear interrupt flag TMR1H=0xFF; //Re-load TMR1H and TMR1L TMR1L=0xF2; } } } void pic_init(void) { TRISB=0b00000000; PORTB=0b00000000; } void timer_init(void) { T1CON=0b00000000; TMR1H=0xFF; TMR1L=0xF2; }

26. Example 2: Circuit Layout

27. Example 2: Simulation Result

28. 1 2 13 14 FFF2 FFF3 FFF4 FFFE FFFF 0000 TMR0IF=0 TMR0IF=0 TMR0IF=0 TMR0IF=0 TMR0IF=0 TMR0IF=1 Example 2: Analysis • Timer1 counts up from FFF2, FFF3, FFF4,….,FFFFH. • From FFFFH to 0000H, TMR1IF is set to 1. • T = 4/10MHz = 0.4s (Each tick consume 0.4s). • How many tick? (FFFF-FFF2) + 1 = 14 Decimal ticks. • Time delay = 14 x 0.4s = 5.6s for half the pulse

29. Delay Calculation • In Hex • (FFFF-FFF2+1)x0.4s • FFF2 are TMR1H and TMR1L initial values(in Hex). b) In Decimal (65536-65523+1)x0.4s 65523 are TMR1H and TMR1L initial values(in Decimal). • General formula for delay calculation • T = 4/(10MHz) = 0.4second

30. 16-bit register timer delay • If we know the amount of timer delay, we find the initial values needed for the TMR1H and TMR1L registers. • From example 2(no prescaler): • T = 4/(10MHz) = 0.4second. • (FFFF-N+1)x0.4s=5.6s. • Whereby N is equal to FFF2H or 65523d.

31. Example 3 • Write a program to generate a square wave with a period of 10ms on pin PORTB.3. Without prescaler and Fosc= 10 MHz. • Solution: • (FFFF-N+1)x(4/10Mhz)=5ms(5ms low and 5ms high). • Therefore N should be CF2CH or 53036d; need to use 16-bit timer module since N is greater than 8-bit. • If Timer0 chosen, N should be divided by 256(prescaler).

32. Example 3: Program #include <htc.h> __CONFIG (FOSC_HS & WDTE_OFF & PWRTE_OFF & BOREN_OFF & LVP_OFF); #define _XTAL_FREQ 10000000 #define LED3 RB3 void pic_init(void); void timer_init(void); main() { pic_init(); //initialize PIC timer_init(); //initialize Timer Module while(1) { T1CON=0b00000001; //start Timer1 if(PIR1==0b00000001) { T1CON=0b00000000; //off Timer1 LED3 = !LED3; PIR1=0b00000000; TMR1H=0xCF; TMR1L=0x2C; }

33. Example 3: Program } } void pic_init(void) { TRISB=0b00000000; PORTB=0b00000000; } void timer_init(void) { T1CON=0b00000000; TMR1H=0xCF; TMR1L=0x2C; }

34. Example 3: Circuit Layout

35. Example 3: Simulation Result

36. Prescaler and generating larger delay XTAL Osc ÷ 4 ÷ 64 TMRx 9-36 • The size of delay depend on • The Crystal frequency • The timer’s bit register. • The largest timer happens when TMR1L=TMR1H=0 • Prescaler option is used to duplicate the delay by dividing the clock by a factor of 2,4,8,16,32,64 ,128,256. • If OPTION_REG =0000 0101, then T = 4*64/f.

37. Counter Programming • Used to counts event outside the PIC • Increments the TMR0 registers • T0CS in T0CON reg. determines the clock source, • If T0CS = 1, the timer is used as a counter • Counts up as pulses are fed from pin RA4 (T0CKI) • What does T0CON=0110 1000 mean? • If TMR1CS=1, the timer 1 counts up as clock pulses are fed into pin RC0

38. Using external Crystal for Timer1 clock • Timer1 comes with two options, • clock fed into T1CKI • T1OSCEN=0 • Clock from a crystal connected to T1OSI-T1OSO (additional) • T1OSCEN=1 • 32 kHz Crystal is connected • Used for saving power during SLEEP mode  doesn’t disable Timer1 while the main crystal is shut down

39. Timer clock source External Source Internal Source 39

40. Example 4 • Write a counter program for 8-bit mode to count the pulses and display the state of 8-bit timer on PORTB.

41. Example 4: Program #include <htc.h> __CONFIG (FOSC_HS & WDTE_OFF & PWRTE_OFF & BOREN_OFF & LVP_OFF); #define _XTAL_FREQ 10000000 void pic_init(void); void timer_init(void); main() { pic_init(); //initialize PIC timer_init(); //initialize Timer Module while(1) { OPTION_REG=0b00100000; //waiting for external input PORTB=TMR0; //TMR0 output through port B if(INTCON==0b00000100) { INTCON=0b00000000; TMR0=0; } } }

42. Example 4: Program void pic_init(void) { TRISA=0b11111111; //whole PortA as input PORTA=0b00000000; //Clear port A TRISB=0b00000000; //whole PortB as output PORTB=0b00000000; //Clear port B } void timer_init(void) { OPTION_REG=0b00100000; //Timer0 external input, prescale 1:2 TMR0=0; }

43. Example 4: Circuit layout

44. Example 4: Simulation Result

45. References • Jie Hu , ECE692 Embedded Computing Systems , Fall 2010. • PIC Microcontroller And Embedded Systems: using Assembly and C for PIC 18, M. Mazidi, R. McKinlay and D. Causey, Prentice Fall, 2008. • Eng. Husam Alzaq, Embedded System Course, IUG, 2010 45