How do I change the polarity of the PWM output, WGM mode 5, OCR1A on the
fly?
I use WGM mode 5 to provide PWM to drive gearhead motors. I update the
OCR values every 50 msec. The algorithm makes changes gradually.
If, for example, the motor is CCW at 50%, the OCR value is 128. The
register values for this are:
(1)
TCCR1A = _BV(COM1A1) | _BV(WGM10);
TCCR1B = _BV(WGM12) | _BV(CS11);
OCR1A = 80;
I want to reverse the direction of the motor. The register values are:
(2)
TCCR1A = _BV(COM1A1) | _BV(COM1A0) |_BV(WGM10);
TCCR1B = _BV(WGM12) | _BV(CS11);
OCR1A = 80;
The algorithm will slow the motor to stop and then reverse it. I tried
setting OCR1A = 0, changing the TCCR1 values, and setting OCR1A = 80.
This does not work. After changing from (1) to (2), the PWM stops.
What am I doing wrong? Any ideas?
Tom Dean
#include <avr/io.h> /* ports and registers */
#include <trace.h>
void motor_init(void);
void both_motor_fwd(void);
void both_motor_rev(void);
void initialize(void);
void initialize() {
TRACE_PORT_DDR = ALL_OUT;
TRACE_PORT = 0;
}
void both_motor_fwd() {
TCCR1A = _BV(COM1A1) | _BV(COM1B1) | _BV(WGM10);
TCCR1B = _BV(WGM12) | _BV(CS11);
TIFR |= _BV(TOV1);
OCR1A = 80;
OCR1B = 160;
}
void both_motor_rev() {
TCCR1A = _BV(COM1A1) | _BV(COM1A0) | _BV(COM1B1) | _BV(COM1B0);
TCCR1B = _BV(WGM12) | _BV(CS11);
TIFR |= _BV(TOV1);
OCR1A = 80;
OCR1B = 160;
}
void motor_init() {
DDRB |= _BV(PB6) | _BV(PB5);
TCCR1A = _BV(COM1A1) | _BV(COM1B1) | _BV(WGM10);
TCCR1B = _BV(WGM12) | _BV(CS11);
OCR1A = 80;
OCR1B = 160;
}
int main() {
initialize();
motor_init();
TIFR |= _BV(TOV1);
while (1) {
TRACE_ON(0);
while ((TIFR & _BV(TOV1)) == 0) ;
TIFR |= _BV(TOV1);
//both_motor_rev();
TRACE_ON(1);
while ((TIFR & _BV(TOV1)) == 0) ;
TIFR |= _BV(TOV1);
TRACE_OFF(1);
TRACE_OFF(0);
//both_motor_fwd();
}
return 0;
}
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