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Kevin |
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#include "PWM.h"
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#include "INTERRUPTS.h"
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static volatile uint8_t computedFrequency = 0;
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static volatile uint8_t computedDutyCycleHigh_UpperByte = 0;
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static volatile uint8_t computedDutyCycleHigh_LowerBits = 0;
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static volatile uint8_t computedDutyCycleLow_UpperByte = 0;
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static volatile uint8_t computedDutyCycleLow_LowerBits = 0;
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static volatile uint8_t savedDutyCycleHigh = PWM_DEFAULT_HIGH_CYCLE;
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static volatile uint8_t savedDutyCycleLow = PWM_DEFAULT_LOW_CYCLE;
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static volatile uint16_t savedPattern = 0xAAAA;
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void PWM_Init() {
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// Initialize CCP1 / Timer 2
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CCP1_TRIS = 1; // PWM output starts disabled
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CCP1CONbits.P1M = 0b00; // Single output, P1A modulated only
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CCP1CONbits.CCP1M = 0b1100; // PWM Mode, P1A active-high, P1B active-high
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PIR1bits.TMR2IF = 0; // Clear Timer 2 interrupt flag
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TMR2 = 0x0;
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Set_PWM_Frequency(PWM_DEFAULT_FREQ);
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Set_PWM_Duty_Cycle(PWM_DEFAULT_HIGH_CYCLE, PWM_DEFAULT_LOW_CYCLE);
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}
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void Set_PWM_Frequency(uint32_t frequency) {
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// Timer 2 clocked at FOSC/4 (20 Mhz)
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// Prescaler 1:1 = minimum frequency of 19,532 Hz
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// Prescaler 1:4 = minimum frequency of 4,883 Hz
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// Prescaler 1:16 = minimum frequency of 1,221 Hz
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// Prescaler 1:64 = minimum frequency of 306 Hz
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// PWM Period = [PR2 + 1] * 4 * TOSC * Prescale
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// = [PR2 + 1] * 4 * (1/FOSC) * Prescale
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// = ([PR2 + 1] * 4 * Prescale) / FOSC
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// PWM Freq = 1/(PWM Period)
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// = 1/(PR2 + 1) * 1/4 * FOSC * 1/Prescale)
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// = FOSC / ([PR2 + 1] * 4 * Prescale)
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// PR2 = (FOSC / [(PWM Freq) * 4 * Presccale]) - 1
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uint8_t preScaleValue;
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if (frequency > 19532) {
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preScaleValue = 1;
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T2CONbits.T2CKPS = 0b00;
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} else if (frequency > 4883) {
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preScaleValue = 4;
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T2CONbits.T2CKPS = 0b01;
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} else if (frequency > 1221) {
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preScaleValue = 16;
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T2CONbits.T2CKPS = 0b10;
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} else {
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preScaleValue = 64;
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T2CONbits.T2CKPS = 0b11;
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}
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uint32_t tmp = frequency * 4 * preScaleValue;
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computedFrequency = (_XTAL_FREQ / tmp) - 1;
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// Updated duty cycle
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Set_PWM_Duty_Cycle(savedDutyCycleHigh, savedDutyCycleLow);
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}
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void Set_PWM_Duty_Cycle(uint8_t highPercent, uint8_t lowPercent) {
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// Duty cycle specified by 10 bit value in CCPR1L:DC1B<1:0>
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savedDutyCycleHigh = highPercent;
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savedDutyCycleLow = lowPercent;
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// Compute values to store in register
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uint32_t highValue = (computedFrequency + 1) * 4;
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highValue *= highPercent;
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highValue /= 100;
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computedDutyCycleHigh_LowerBits = highValue & 0x3;
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computedDutyCycleHigh_UpperByte = (highValue >> 2) & 0xFF;
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uint32_t lowValue = (computedFrequency + 1) * 4;
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lowValue *= lowPercent;
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lowValue /= 100;
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computedDutyCycleLow_LowerBits = lowValue & 0x3;
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computedDutyCycleLow_UpperByte = (lowValue >> 2) & 0xFF;
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}
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void Set_PWM_Pattern(uint16_t pattern) {
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savedPattern = pattern;
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}
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void PWM_Transmit_Pattern() {
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// Set PWM frequency pre-computed values
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PR2 = computedFrequency;
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// Set duty cycle to 0%
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CCP1CONbits.DC1B = 0b00;
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CCPR1L = 0x00;
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// Start timer and wait for it to rollover to latch duty cycle value
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T2CONbits.TMR2ON = 1;
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while (!PIR1bits.TMR2IF);
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PIR1bits.TMR2IF = 0;
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CCP1_TRIS = 0;
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// Bit 15
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if (savedPattern & 0x8000) {
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CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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CCPR1L = computedDutyCycleLow_UpperByte;
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}
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while (!PIR1bits.TMR2IF);
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PIR1bits.TMR2IF = 0;
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/* The above section of code disassembles to the following assembly code
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* According to the instruction set table, this should take 22 cycles to execute
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* 22 cycles corresponds to a maximum of ~227.272 kHz PWM frequency
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* If higher PWM frequency is needed, DC1B can be omitted for lower duty cycle accuracy
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! if (pattern & 0x8000) {
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0x26: BTFSS 0x72, 0x7
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0x27: GOTO 0x34
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! CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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0x28: MOVLB 0x0
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0x29: MOVF computedDutyCycleHigh_LowerBits, W
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0x2A: MOVWF 0x73
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0x2B: SWAPF 0x73, F
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0x2C: MOVLB 0x5
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0x2D: MOVF CCP1CON, W
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0x2E: XORWF 0x2F3, W
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0x2F: ANDLW 0xCF
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0x30: XORWF 0x2F3, W
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0x31: MOVWF CCP1CON
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! CCPR1L = computedDutyCycleHigh_UpperByte;
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0x32: MOVF computedDutyCycleHigh_UpperByte, W
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0x33: GOTO 0x41
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! } else {
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! CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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0x34: MOVLB 0x0
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0x35: MOVF computedDutyCycleLow_LowerBits, W
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0x36: MOVWF 0x73
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0x37: SWAPF 0x73, F
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0x38: MOVLB 0x5
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0x39: MOVF CCP1CON, W
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0x3A: XORWF 0x2F3, W
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0x3B: ANDLW 0xCF
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0x3C: XORWF 0x2F3, W
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0x3D: MOVWF CCP1CON
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! CCPR1L = computedDutyCycleLow_UpperByte;
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0x3E: MOVLB 0x0
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0x3F: MOVF computedDutyCycleLow_UpperByte, W
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0x40: MOVLB 0x5
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0x41: MOVWF CCPR1
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! }
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! while (!PIR1bits.TMR2IF);
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0x42: MOVLB 0x0
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0x43: BTFSS PIR1, 0x1
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0x44: GOTO 0x42
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! PIR1bits.TMR2IF = 0;
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0x45: BCF PIR1, 0x1
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155 |
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* If DC1B is ignored, the disassembly is as follows:
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* According to the instruction set table, this should take 14 cycles to execute
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* 14 cycles corresponds to a maximum of ~357.142 kHz PWM frequency
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! // Bit 15
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! if (pattern & 0x8000) {
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0x26: BTFSS 0x72, 0x7
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0x27: GOTO 0x2A
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! CCPR1L = computedDutyCycleHigh_UpperByte;
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0x28: MOVF computedDutyCycleHigh_UpperByte, W
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0x29: GOTO 0x2C
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! } else {
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! CCPR1L = computedDutyCycleLow_UpperByte;
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0x2A: MOVLB 0x0
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0x2B: MOVF computedDutyCycleLow_UpperByte, W
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0x2C: MOVLB 0x5
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0x2D: MOVWF CCPR1
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! }
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! while (!PIR1bits.TMR2IF);
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0x2E: MOVLB 0x0
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0x2F: BTFSS PIR1, 0x1
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0x30: GOTO 0x2E
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! PIR1bits.TMR2IF = 0;
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0x31: BCF PIR1, 0x1
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*/
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// Bit 14
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if (savedPattern & 0x4000) {
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CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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CCPR1L = computedDutyCycleLow_UpperByte;
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}
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while (!PIR1bits.TMR2IF);
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PIR1bits.TMR2IF = 0;
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// Bit 13
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if (savedPattern & 0x2000) {
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CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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CCPR1L = computedDutyCycleLow_UpperByte;
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}
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while (!PIR1bits.TMR2IF);
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PIR1bits.TMR2IF = 0;
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// Bit 12
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if (savedPattern & 0x1000) {
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CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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CCPR1L = computedDutyCycleLow_UpperByte;
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}
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while (!PIR1bits.TMR2IF);
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PIR1bits.TMR2IF = 0;
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// Bit 11
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if (savedPattern & 0x0800) {
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CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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CCPR1L = computedDutyCycleLow_UpperByte;
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}
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while (!PIR1bits.TMR2IF);
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PIR1bits.TMR2IF = 0;
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// Bit 10
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if (savedPattern & 0x0400) {
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CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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CCPR1L = computedDutyCycleLow_UpperByte;
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}
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while (!PIR1bits.TMR2IF);
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PIR1bits.TMR2IF = 0;
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// Bit 9
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if (savedPattern & 0x0200) {
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CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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CCPR1L = computedDutyCycleLow_UpperByte;
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}
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while (!PIR1bits.TMR2IF);
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PIR1bits.TMR2IF = 0;
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246 |
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// Bit 8
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if (savedPattern & 0x0100) {
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CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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252 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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CCPR1L = computedDutyCycleLow_UpperByte;
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}
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255 |
while (!PIR1bits.TMR2IF);
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256 |
PIR1bits.TMR2IF = 0;
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257 |
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258 |
// Bit 7
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259 |
if (savedPattern & 0x0080) {
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260 |
CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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261 |
CCPR1L = computedDutyCycleHigh_UpperByte;
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} else {
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263 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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264 |
CCPR1L = computedDutyCycleLow_UpperByte;
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}
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266 |
while (!PIR1bits.TMR2IF);
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267 |
PIR1bits.TMR2IF = 0;
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268 |
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269 |
// Bit 6
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270 |
if (savedPattern & 0x0040) {
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271 |
CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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272 |
CCPR1L = computedDutyCycleHigh_UpperByte;
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273 |
} else {
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274 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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275 |
CCPR1L = computedDutyCycleLow_UpperByte;
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276 |
}
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277 |
while (!PIR1bits.TMR2IF);
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278 |
PIR1bits.TMR2IF = 0;
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279 |
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280 |
// Bit 5
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281 |
if (savedPattern & 0x0020) {
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282 |
CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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283 |
CCPR1L = computedDutyCycleHigh_UpperByte;
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284 |
} else {
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285 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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286 |
CCPR1L = computedDutyCycleLow_UpperByte;
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287 |
}
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288 |
while (!PIR1bits.TMR2IF);
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289 |
PIR1bits.TMR2IF = 0;
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290 |
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291 |
// Bit 4
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292 |
if (savedPattern & 0x0010) {
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293 |
CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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294 |
CCPR1L = computedDutyCycleHigh_UpperByte;
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295 |
} else {
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296 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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297 |
CCPR1L = computedDutyCycleLow_UpperByte;
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298 |
}
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299 |
while (!PIR1bits.TMR2IF);
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300 |
PIR1bits.TMR2IF = 0;
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301 |
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302 |
// Bit 3
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303 |
if (savedPattern & 0x0008) {
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304 |
CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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305 |
CCPR1L = computedDutyCycleHigh_UpperByte;
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306 |
} else {
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307 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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308 |
CCPR1L = computedDutyCycleLow_UpperByte;
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309 |
}
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310 |
while (!PIR1bits.TMR2IF);
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311 |
PIR1bits.TMR2IF = 0;
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312 |
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313 |
// Bit 2
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314 |
if (savedPattern & 0x0004) {
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315 |
CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
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316 |
CCPR1L = computedDutyCycleHigh_UpperByte;
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317 |
} else {
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318 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
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319 |
CCPR1L = computedDutyCycleLow_UpperByte;
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|
|
320 |
}
|
|
|
321 |
while (!PIR1bits.TMR2IF);
|
|
|
322 |
PIR1bits.TMR2IF = 0;
|
|
|
323 |
|
|
|
324 |
// Bit 1
|
|
|
325 |
if (savedPattern & 0x0002) {
|
|
|
326 |
CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
|
|
|
327 |
CCPR1L = computedDutyCycleHigh_UpperByte;
|
|
|
328 |
} else {
|
|
|
329 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
|
|
|
330 |
CCPR1L = computedDutyCycleLow_UpperByte;
|
|
|
331 |
}
|
|
|
332 |
while (!PIR1bits.TMR2IF);
|
|
|
333 |
PIR1bits.TMR2IF = 0;
|
|
|
334 |
|
|
|
335 |
// Bit 0
|
|
|
336 |
if (savedPattern & 0x0001) {
|
|
|
337 |
CCP1CONbits.DC1B = computedDutyCycleHigh_LowerBits;
|
|
|
338 |
CCPR1L = computedDutyCycleHigh_UpperByte;
|
|
|
339 |
} else {
|
|
|
340 |
CCP1CONbits.DC1B = computedDutyCycleLow_LowerBits;
|
|
|
341 |
CCPR1L = computedDutyCycleLow_UpperByte;
|
|
|
342 |
}
|
|
|
343 |
while (!PIR1bits.TMR2IF);
|
|
|
344 |
PIR1bits.TMR2IF = 0;
|
|
|
345 |
|
|
|
346 |
// Set next duty cycle to 0% (idle line low)
|
|
|
347 |
CCP1CONbits.DC1B = 0b00;
|
|
|
348 |
CCPR1L = 0x00;
|
|
|
349 |
|
|
|
350 |
// Wait for timer to rollover, then turn off timer
|
|
|
351 |
while (!PIR1bits.TMR2IF);
|
|
|
352 |
PIR1bits.TMR2IF = 0;
|
|
|
353 |
T2CONbits.TMR2ON = 0;
|
|
|
354 |
TMR2 = 0x0;
|
|
|
355 |
}
|