Using Timer1 and CCP
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Timers 1, 3, and 5 of the PIC18 microcontroller family are versatile 16-bit timers that can be clocked from various sources and prescaled. They support overflow interrupts and gating. The PIC18 also includes 5 Capture-Compare-PWM (CCP) modules that can be configured to operate in capture, compare, or PWM modes to interact with the timers in hardware without interrupts. Each CCP module is associated with a pin and selectable timer.
Using Timer1 and CCP
- 1. Using Timer1/3/5 and the Capture-Compare-PWM Circuit Corrado Santoro ARSLAB - Autonomous and Robotic Systems Laboratory Dipartimento di Matematica e Informatica - Universit`a di Catania, Italy santoro@dmi.unict.it L.A.P. 1 Course Corrado Santoro Using Timer1/3/5 and CCP
- 2. The other timers of of PIC18 In addition to TIMER0, PIC18 Family has other 6 timers, subdivided in two families First family includes TIMER1, TIMER3 and TIMER5 Second family includes TIMER2, TIMER4 and TIMER6 Timers of the same family have the same structure and working scheme Corrado Santoro Using Timer1/3/5 and CCP
- 3. The timers 1/3/5 of of PIC18 These timers are more versatile than the others and, therefore, are a little bit more complex: 16-bit timers Clock source selectable from: FOSC FOSC/4 External input Secondary oscillator module Prescaler with division by 1, 2, 4, 8; Overflow (0xFFFF → 0) triggers an interrupt. Gated timers, i.e. counting can be enabled by: Bit TMRxON (as in other timers) External input TxG Specific event source coming from other peripherals Corrado Santoro Using Timer1/3/5 and CCP
- 4. The timers 1/3/5 of of PIC18 Corrado Santoro Using Timer1/3/5 and CCP
- 5. Control Register of timers 1/3/5 TMRxCS: Clock source select 00, FOSC/4 01, FOSC 10 & TxSOSCEN = 0, External clock from TxCKI pin 11 & TxSOSCEN = 1, Clock from external crystal TxCKPS: Prescaler setup 00 = 1:1 prescaler 01 = 1:2 prescaler 10 = 1:4 prescaler 11 = 1:8 prescaler TxRD16: 16-bit R/W Operations TMRxON: Timer On/Off control Corrado Santoro Using Timer1/3/5 and CCP
- 6. Gate Control Register of timers 1/3/5 TMRxGE: Gate Enable bit 0, Gate is disabled 1, Gate is enabled and gate function is controlled by other bits Corrado Santoro Using Timer1/3/5 and CCP
- 7. Interrupt flags of timers 1/3/5 Interrupt (overflow) flags of timers 1/3/5 belong to various special function registers: TMR1IF ⇒ PIR1bits.TMR1IF TMR1IE ⇒ PIE1bits.TMR1IE TMR3IF ⇒ PIR2bits.TMR3IF TMR3IE ⇒ PIE2bits.TMR3IE TMR5IF ⇒ PIR5bits.TMR5IF TMR5IE ⇒ PIE5bits.TMR5IE Corrado Santoro Using Timer1/3/5 and CCP
- 8. The Capture-Compare-PWM Circuit (CCP) The CCP is a special circuit which performs certain signal manipulation and measurement functions. It has 3 working modes: Capture: at the occurrence of a pre-programmed edge in an input signal, it takes a snapshot of the value of a timer Compare: when the value of a timer matches a pre-programmed constant, the circuit generates a specific output signal PWM: it generates a PWM signal totally in hardware Capture/Compare events can drive a proper interrupt The 18F25K22 has 5 CCP modules Each one can be programmed to work in one of the three modes above Each CCP module has its specific input/output pin Corrado Santoro Using Timer1/3/5 and CCP
- 9. Capture Mode Input signal is taken from CCPx pin (which is multiplexed with a digital I/O port) The edge detector is able to identify a falling- or rising-edge in the input signal, according to the value of bits CCPxM (CCP Mode) The programmable prescaler is able to identify each edge, each 4th edge or each 16th edge When the (programmed) edge is detected, the value of TIMER1/3/5 is copied into the CCPRx register and (optionally) an interrupt is generated All the process occurs in hardware Corrado Santoro Using Timer1/3/5 and CCP
- 10. Compare Mode CCPx pin acts as output The software can program a value in the CCPRx register When the value of TIMER1/3/5 matches the value in CCPRx one of the following programmed events occurs: The output is set to 0 The output is set to 1 The output is toggled (0 → 1, 1 → 0) An optional interrupt is also generated All the process occurs in hardware Corrado Santoro Using Timer1/3/5 and CCP
- 11. PWM Mode CCPx pin acts as output One of the TIMER2/4/6 is used The PWM period is programmed into the PRx register (timer period register) The duty cycle is programmed into the CCPRx register All the process occurs in hardware Corrado Santoro Using Timer1/3/5 and CCP
- 12. CCP Control Register DCxB: duty cycle bits 8 and 9 (used in PWM Mode) CCPxM: CCP Mode 0000, circuit is off 0010, Compare mode, toggle output on match 1000, Compare mode, “set” output on match 1001, Compare mode, “clear” output on match 0100, Capture mode, every falling edge 0101, Capture mode, every rising edge 0110, Capture mode, every 4th rising edge 0111, Capture mode, every 16th rising edge 11xx, PWM mode Corrado Santoro Using Timer1/3/5 and CCP
- 13. CCP Timer Selection CCPTMRS0 and CCPTMRS1 registers are used to select the timer to use in each CCP circuit. CxTSEL: Timer selection 00, Capture/compare uses Timer1, PWM uses Timer2 01, Capture/compare uses Timer3, PWM uses Timer4 10, Capture/compare uses Timer5, PWM uses Timer6 Corrado Santoro Using Timer1/3/5 and CCP
- 14. Interrupt flags of CCP 1–5 Interrupt (event) flags of CCP circuits from 1 to 5 belong to various special function registers: CCP1IF ⇒ PIR1bits.CCP1IF CCP1IE ⇒ PIE1bits.CCP1IE CCP2IF ⇒ PIR2bits.CCP2IF CCP2IE ⇒ PIE2bits.CCP2IE CCP3IF ⇒ PIR4bits.CCP3IF CCP3IE ⇒ PIE4bits.CCP3IE CCP4IF ⇒ PIR4bits.CCP4IF CCP4IE ⇒ PIE4bits.CCP4IE CCP5IF ⇒ PIR4bits.CCP5IF CCP5IE ⇒ PIE4bits.CCP5IE Corrado Santoro Using Timer1/3/5 and CCP
- 15. CCP Circuit PIN Assignment in PIC18F25K22 CCP1 ⇒ RC2 CCP2 ⇒ RC1 or RB3 (settable through a configuration register) CCP3 ⇒ RC6 or RB5 (settable through a configuration register) CCP4 ⇒ RB0 CCP5 ⇒ RA4 Corrado Santoro Using Timer1/3/5 and CCP
- 16. Using Timer1/3/5 and the Capture-Compare-PWM Circuit Corrado Santoro ARSLAB - Autonomous and Robotic Systems Laboratory Dipartimento di Matematica e Informatica - Universit`a di Catania, Italy santoro@dmi.unict.it L.A.P. 1 Course Corrado Santoro Using Timer1/3/5 and CCP