Timer 0 and Timer 2 are 8 bit timers, while Timer 1 is a 16 bit timer. The ATmega328P has three timers known as Timer 0, Timer 1, and Timer 2. set the COM bits) on that pin in order to get a result. This is because you need to both enable the pin for output and set the PWM mode (i.e. Note that the data sheet states that " using the Output Compare to generate waveforms in Normal mode is not recommended, since this will occupy too much of the CPU time." The main PWM modes are "Fast PWM" and "Phase-correct PWM".Īssuming we haven't changed anything and we are in "Normal" mode, then TOP = 0xFFFF = 65535, and setting 0CR1A to 32767, should deliver PWM with a 50% duty cycle. This is defined in Table 17-2 of the ATmega2560 data sheet (Figure 10). What happens next will be determined by the current mode of operation, which is set by a combination of the Waveform Generation mode and Compare Output mode bits. For D11on the ATmega2560 the register is OCR1A. To adjust the PWM duty cycle, we can modify the appropriate Output Compare Register. Arduino pins and associated Output Compare Register. The association between OCR's and pins for the 2560 is shown in Figure 9.įigure 9. In the data sheet the Output Compare Registers are labelled OCRxA, OCRxB or OCRxC (where x is the timer number 0.5). The assignment is dependent on the mode of operation (Figure 10). The TOP value can be assigned to be one of the fixed values: 0xFFFF, 0x00FF, 0x01FF, or 0x03FF, or to the value stored in the OCRnA or ICRn Register. So for example, to get a 50% duty cycle, you set the OCR to half of the top counter value - referred to as "TOP" in the datasheet. Instead of using analogWrite(), we can manipulate the Output Compare Registers (OCR) directly to adjust the duty cycle. The ATmega2560 has 15 pins which can be used for PWM output. Most of the register based PWM examples available are for the ATmega328P and our version of the MEGA uses the ATmega2560, so you need to make sure that you are using the correct registers and timers for your microprocessor. DDRB is the data direction register for Port B. This line of code sets the 5th bit of the DDRB register to 1 and is equivalent to pinMode(11, OUTPUT). We will use pin D11 (ATmega2560 physical pin 24, Port B bit 5) as this will work for an UNO or MEGA and is our next free pin. It isn't possible to change the frequency using either of the two previous methods.Ĭhanging Pulse Width / Duty Cycle Using Registers Servo Library PWM set to 90 degreesĪlternatively, you can access the Atmel registers directly for finer control, this allows you to change the type, range and frequency of the pulse width modulation (PWM). The servo moves at a set speed (0.1 s/60 degrees for the SG90), regardless of how quickly you change the pulses.įigure 8. There is no point changing the frequency of the control pulses, unless the servo you are testing expects something different to 50 Hz. Whether + or - 90 degrees is left or right will depend on how you mounted the servo. 0 degrees - the centre position with a 1.5 ms pulse.The SG90 expects a frequency of 50 Hz on the control line and the position it moves to depends on the pulse width of the signal. Stall current with 5V supply (horn locked) 650 ☘0mA.Running current with 5V supply (no mechanical load) 220 ±50mA.From this we can determine the following characteristics: We found a more useful Data Sheet at MicoPik. We need the pulse width's required to drive the servo. The Jaycar SG90 Data Sheet only helps with the wiring details.
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