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// PROJECT :PWMTimer1Mode15
// PURPOSE :Hobby Servo control using Register-level commands under Timer1, Mode 15
// DEVICE :Arduino
// AUTHOR :C. D'Arcy
// DATE :2019 03 28
// MCU :328
// STATUS :Working
// REFERENCE:Chapter 16.
#include "prescalers.h"
#define F_CPU 16000000L //MCU Clock frequency
#define PRESCALE 8 //Timer 1 prescale
#define FREQ 50 //desired servo PWM frequency
#define TOP F_CPU/PRESCALE/FREQ //Timer 1, Mode 15 with OCR1A as TOP
#define MIN_DUTY TOP/20 //5% duty cycle (should) place servo horn in home position
#define MAX_DUTY TOP/10 //10% duty cycle (should) place servo horn in max position
#define DEBUG //optional Serial Montoring...
uint8_t potPin = A1; //use a pot to vary the PWM signa's duty cycle (horn position)
uint16_t reading; //variable to read the value from the analog pin
void setup() {
#ifdef DEBUG
while (!Serial);
potSetup(); //Q&D: Pot as Appliance
PWMSetup(); //Timer1 required to get down to 50 Hz in this Mode
void potSetup() {
DDRC = 0b00000101; //Shoulder leads (A&C) configured for output on analog port
PORTC = 0b00000100; //Set one shoulder HIGH, the other remains LOW
void PWMSetup() {
DDRB |= 1 << PB2; //must declare OC1B pin for output
TCCR1A = 1 << COM1B1 | 1 << WGM11 | 1 << WGM10; //contribute to Mode 15,
TCCR1B = 1 << WGM13 | 1 << WGM12 | T1ps8; //complete mode 15, prescale
OCR1A = TOP; //TCNT1 resets when TOP (OCR1A) reached, OC1B is set
OCR1B = MIN_DUTY; //when TCNT1 reaches OCR1B, OC1B pin clears
TCNT1 = 0; //not necessary
void loop() {
#ifdef DEBUG //optional Serial Monitoring
reading = analogRead(potPin); //read the 10-bit pot value
delay(20); //let it settle, to be sure
//scale the pot reading to duty cycle compatible value
OCR1B = map(reading, 0, 1023, MIN_DUTY, MAX_DUTY);
delay(1000); //give the servo time to reach new position
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