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PLT 206 Microcontroller Systems CCP

Learn about the CCP module modes of PIC16 microcontroller systems and how to program them in Hitech-C. Includes a detailed example.

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PLT 206 Microcontroller Systems CCP

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  1. PLT 206Microcontroller SystemsCCP PIC16 Timer Programming in Hitech-C

  2. Today’s Lecture • List the CCP module/s of PIC16 and their associated registers. • Describe the various modes of the PIC16 CCP module. • Program the PIC16 CCP module in ‘Hitech C’.

  3. Introduction • Stands for Capture/Compare/PWM. • Allows the user to time and control different events. • The (CCP) module is a programmable software able to operate in one of the three modes: • A Capture input • A Compare output • A Pulse Width Modulation (PWM).

  4. Introduction • PIC 16F CCP resource :

  5. Capture • Consider a stop watch • You start the stop watch • The stop watch runs while you wait for an event(s) to happen • Once the event(s) happen the stop watch is stopped and the time is recorded • For the PIC • Timer 0, Timer 1 or Timer 2 start • An event occurs on the CCPxpin • A the moment the event occurs the time is captured and stored in CCPRxH:CCPRxL • The contents of an internal 16 bit timer, upon detecting an n-th rising or falling edge, to be written to on-board special function registers Figure 1

  6. Compare • Consider your alarm clock • When the time is 07:00 the alarm goes off. • This is a compare of the current time with a stored time. • If the two match then an event (the alarm goes off) happens. • For the PIC • When the value of timer1 matches what is stored in CCPR1H:CCPR1L the CCP1 pin output is changed and the CCP1IF bit is set. • Timer2 and CCP2 can also be used for this purpose. • Generates an interrupt, or change on output pin, when Timer 1 matches a pre-set comparison value. Figure 2

  7. Pulse Width Modulation (PWM) • Creates a re-configurable square wave duty cycle output at a user set frequency. • The higher duty cycle, the better performance of an output. Figure 3

  8. CCP resources : • Single source clocks for Capture and Compare or PWM modes. • Two separate CCP Modules(CCP1 and CCP2). • Each CCP module supports Capture, Compare or PWM modes

  9. CCP1 Module • 16-bit register. • Consists of the CCPR1L and CCPR1H registers. • Used for capturing or comparing with binary number stored in the timer register TMR1 (TMR1H and TMR1L). Figure 4

  10. CCP1 Module • The CCP1CON register controls the operation of CCP1. • CCP Register nomenclature • CCPxCON == CCP1CON or CCP2CON • CCPxSTAT == CCP1STAT or CCP2STAT • CCPxL == CCP1L or CCP2L • CCPxH == CCP1H or CCP2H

  11. CCP1 Module

  12. CCP1 Module

  13. CCP2 Module • CCP1 and CCP2 modules are identical in operation. • Difference exist when CCP2 operates in Compare mode. • Timer1 reset signal will automatically start A/D conversion (if enabled).

  14. CCP2 Module

  15. Capture input • CCP pin is set to input and monitored for a change of state: • Every falling edge • Every rising edge • Every 4th rising edge • Every 16th rising edge • Upon detecting an nth rising or falling edge, timer register value(16-bit) is copied to the CCP register. • Allows timing for the duration of an event.

  16. Capture input • Example • If CCP1CON = 0b00000101; • Every rising edge • Low-to-High transition • Timer1 must be turned on as continuous clock source, T1CON= 0b00000001;

  17. Programming in capture mode • Initialize CCP1CON for compare. CCP1CON=0b00000100; //Capture rising edge • CCP1 as input pin. TRISC=0b00000100; //Portc bit 2 as input • Initialize T1CON for capture. T1CON=0b00000000; //T1CON for capture • Read register value on the first rising edge and save it. • Read register value on the second rising edge and save it. • Subtract the value in step 4 from the value in step 3.

  18. Example 1 • Write a program to measure the period of the pulse being fed to CCP pin. PORTB CCP1(RC2) PORTC PIC16F877A PORTD Figure 5

  19. Example 1: 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); void ccp_init(void); main() { pic_init(); //initialize PIC timer_init(); //initialize Timer Module ccp_init(); //initialize CCP Module while(1) { while(PIR1bits.CCP1IF==0) { T1CON=0b00000001; //start Timer1 PIR1=0b00000000; }

  20. Example 1: Program while(PIR1bits.CCP1IF==1) { T1CON=0b00000000; //stop Timer1 PIR1bits.CCP1IF=0; PORTB=CCPR1L; PORTD=CCPR1H; } } } void pic_init(void) { TRISB=0b00000000; PORTB=0b00000000; TRISC=0b11111111; PORTC=0b00000000; TRISD=0b00000000; PORTD=0b00000000; }

  21. Example 1: Program void timer_init(void) { T1CON=0b00000000; PIR1=0b00000000; TMR1H=0; TMR1L=0; } void ccp_init(void) { CCP1CON=0b00000100; //Capture rising edge CCPR1H=0; CCPR1L=0; }

  22. Example1: Simulation Result • When clock at 150cyc low and 150cyc high, PIR will interrupt at CCPR1L = DFH (high to low). Figure 8 Figure 7 Figure 9

  23. Example1: Simulation Result • After 2nd cycle • PIR will interrupt at CCPR1H=2H and CCPR1L=0BH. Figure 10 Figure 11

  24. Example1: Simulation Result • Subtracting these two values: • 20BH-DFH=12CH→300d Figure 12

  25. Compare input • Generate an interrupt, or change on output pin, when Timer1 matches a pre-set comparison value. • Load initial values to Timer1(TMR1H:TMR1L) and CCPRxH:CCPRxL. • Timer1(TMR1H:TMR1L) value counts up and constantly compared with CCPRxH:CCPRxL. • When match occurs CCP will perform(Event trigger Options): • Low to High Transition • High to Low Transitions • Interrupt Request Without Pin Change • Trigger Special Event

  26. Compare input • Example • If CCP1CON=0b00001000; • Compare mode • Set output (CCP1IF bit is set) upon match. • Timer1 must be turned on as continuous clock source, T1CON= 0b00000001;

  27. Programming in compare mode • Initialize CCP1CON for compare. CCP1CON=0b00001000; //Compare mode • CCP1 as input pin. TRISC=0b00000100; //Portc bit 2 as input • Initialize T1CON for compare. T1CON=0b00000000; //T1CON for compare • Start Timer1. T1CON=0b00000001; //Start Timer1 • Monitor the CCP1IF flag.

  28. Example 2 • Write a program to compare the period of the pulse being fed to CCP pin. LED CCP1(RC2) T1CKI(RC0) PIC16F877A Figure 13

  29. Example 2: Program #include <htc.h> __CONFIG (FOSC_HS & WDTE_OFF & PWRTE_OFF & BOREN_OFF & LVP_OFF); #define _XTAL_FREQ 10000000 #define LED0 RD0 void pic_init(void); void timer_init(void); void ccp_init(void); main() { pic_init(); //initialize PIC timer_init(); //initialize Timer Module ccp_init(); while(1)

  30. Example 2: Program { T1CON=0b0000011; //start Timer1 if(PIR1bits.CCP1IF==1) { T1CON=0b00000010; //stop Timer1 PIR1bits.CCP1IF=0; TMR1H=0; TMR1L=0; } } } void pic_init(void)

  31. Example 2: Program { TRISB=0b00000000; PORTB=0b00000000; TRISC=0b00000001; PORTC=0b00000000; TRISD=0b00000000; PORTD=0b00000000; } void timer_init(void) { T1CON=0b00000010; PIR1=0b00000000;

  32. Example 2: Program TMR1H=0x00; TMR1L=0x00; } void ccp_init(void) { CCP1CON=0b00001000; //compare mode CCPR1H=0x00; CCPR1L=0x08; }

  33. Example 2: Simulation Result CCP1 high after 8 pulse Figure 14

  34. Example 2: Simulation Result • CCPR1H and CCPR1L are loaded with 0008H. • When timer1 starts count, TMR1L and TMR1H will increments. These values will be constantly compared with CCPR1H and CCPR1L. • If match, CCP1IF will be set to ‘1’, thus making CCP1(RC2) High.

  35. PWM • Create pulses with variable widths. • A PWM output is basically a square waveform with a specified period and duty cycle. • The pulse width modulation (PWM) mode produces a PWM output. • CCPx pin produces up to a 10-bit resolution PWM output. Figure 15

  36. PWM - Period • The PWM period is specified by writing to the PR2 register. • The PWM period can be calculated using the following formula: • PWM Period = [(PR2) + 1] • 4 • TOSC •(TMR2 Prescale Value) • Where: • PR2 is the value loaded into Timer 2 register • TMR2PS is the Timer 2 prescaler value • TOSC is the clock oscillator period (seconds) • The PWM frequency is defined as 1/(PWM period).

  37. PWM - Period • Example: • If XTAL=20MHz and FPWM = 1.22kHz; • PR2 = 4,097 – which is larger than 256(8bit) • Reducing the FOSC through prescaler value (set to 16) • PR2 = 255

  38. PWM - Duty Cycle • Portion of pulse that stays HIGH relative to the entire period. • Supports up to 10 bit resolution. • CCPx pin TRIS bit must be cleared to configure the pin as output. • PWM mode is enabled by placing CCPxM3:CCPxM0 = b’11xx. • Specified by writing to the CCPR1L register and to the CCP1CON<5:4> bits. • The CCPR1L contains the eight LSbs and the CCP1CON<5:4> contains the two MSbs.

  39. PWM - Duty Cycle • The following equation is used to calculate the PWM duty cycle in time: • PWM Duty Cycle =(CCPR1L:CCP1CON<5:4>) •TOSC • (TMR2 Prescale Value)

  40. Programming in PWM mode • Set PWM period through PR2 register. PR2=0x37; • Set PWM duty cycle through CCPR1L for the first 8-bits. CCPR1L=0b00011011; • Set CCP pin as an output. TRISCbits.CCP1=0; • Set prescale value through T2CON. T2CON= 0b00000000; • Clear TMR2 register. TMR2=0;

  41. Programming in PWM mode • Configure CCP1CON for PWM, CCPxX and CCPxY for the remaining 10-bits CCP1CON=0b00001100; • Start Timer2. T2CON=0b00000101;

  42. Example 3 • PWM pulses must be generated from pin CCP1 of a PIC16F877A microcontroller. The required pulse period is 44s and the required duty cycle is 50%. Assuming that the microcontroller operates with a 20MHz crystal, calculate the values to be loaded into the various registers • TOSC = 1/20MHz = 5x10-8s • PWM duty cycle is 44s/2 = 22s.

  43. Example 3 CCPR1L:CCP1CON<5:4> • Which is equivalent to 10-bit binary : “00 01101 110” PWM Mode XX101100 CCP1CON=0b00101100; CCPR1L=0b00011011

  44. Example 3 - Program #include <htc.h> __CONFIG (FOSC_HS & WDTE_OFF & PWRTE_OFF & BOREN_OFF & LVP_OFF); #define _XTAL_FREQ 20000000 void pic_init(void); void timer_init(void); void ccp_init(void); main() { pic_init(); //initialize PIC timer_init(); //initializeTimer Module ccp_init(); while(1)

  45. Example 3 - Program { T2CON=0b00000101; //start Timer2 while(PIR1bits.TMR2IF==0) { PIR1bits.TMR2IF=0; } } } void pic_init(void) { TRISC=0b00000000; PORTC=0b00000000; }

  46. Example 3 - Program void timer_init(void) { T2CON=0b00000000; PR2=0x36; TMR2=0; } void ccp_init(void) { CCPR1L=0b00011011; CCP1CON=0b00101100; //PWM mode }

  47. Example 3 - Simulation Result Figure 17

  48. Example 3 - Simulation Result Figure 18

  49. References • PIC16F87XA Data Sheet, Microchip Technology Incorporated, 2003. • PIC Microcontroller And Embedded Systems: using Assembly and C for PIC 18, M. Mazidi, R. McKinlay and D. Causey, Prentice Fall, 2008. • Advanced Pic Micro Controller Projects in c: From Usb to Rtos With the Pic 18f Series, Dogan Ibrahim, Elsevier Ltd, 2008.

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