PV198 – One-chip Controllers, PWM / Dávid Danaj
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PV198 – One-chip Controllers
PWM

PV198 – One-chip Controllers, PWM / Dávid Danaj
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Content
1.What is PWM
2.What is it used for
3.How does it work
4.PWM on FRDM-K66F
1.Timer/PWM Module (TPM)
5.Code
6.Application

PV198 – One-chip Controllers, PWM / Dávid Danaj
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What is PWM
§PWM – Pulse Width Modulation
§A method of reducing the average power delivered by an electrical signal, by effectively chopping
it up into discrete parts

PV198 – One-chip Controllers, PWM / Dávid Danaj
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What is it used for
§Motor control
§Audio amplifiers
§Digital lighting

PV198 – One-chip Controllers, PWM / Dávid Danaj
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How does it work
§Switching fast enough for
the application (low period)
§Changing duty cycle
https://en.wikipedia.org/wiki/Pulse-width_modulation#/media/File:Duty_Cycle_Examples.png
CC BY-SA 4.0

PWM on FRDM-K66F
§FlexTimer Module (FTM)
§4 instances
§2 - 8 channels
§Timer/PWM Module (TPM)
§2 instances
§2 channels
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Timer/PWM Module (TPM)
§Modes of operation:
§Input capture
§Output compare
§Edge-Aligned PWM
§Center-Aligned PWM
§Combine PWM
§Combine Input Capture
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Input capture
§Detects edge in the input signal
§Configurable rising/falling edge detection
§Edge sets interrupt flag
§Read precise time from counter
§Example: ultrasonic distance sensor demo
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Output compare
§Generate timed pulses with programmable
position, polarity, duration, and frequency
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Edge-Aligned PWM
§Leading edge is aligned with the beginning of the period
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Center-Aligned PWM
§Counts up until it reaches MOD and then counts down until it reaches zero
§The pulse width center is when the TPM counter = 0
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Center-Aligned PWM
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Combine PWM
§Even channel (n) and adjacent odd channel (n+1) are combined to generate a PWM signal in the
channel (n) output.
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Combine PWM
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Combine Input Capture
§Measure a pulse width of the signal
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Application
§Create an application that turns on Blue LED with 20% intensity
§Use TPM or FTM peripheral
§Update your application to turn on Green and Red LED with 20% intensity (use FTM, because TPM is
not available)
PV198 – One-chip Controllers, PWM / Dávid Danaj
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Code
const tpm_chnl_pwm_signal_param_t TPM_edge_pwmSignalParams[] = {
  {
    .chnlNumber = kTPM_Chnl_1,
    .level = kTPM_LowTrue,
    .dutyCyclePercent = 20
  }
};
void TPM_edge_init(void) {
  TPM_Init(TPM_EDGE_PERIPHERAL, &TPM_edge_config);
  TPM_SetupPwm(TPM_EDGE_PERIPHERAL, TPM_edge_pwmSignalParams, sizeof(TPM_edge_pwmSignalParams) /
sizeof(tpm_chnl_pwm_signal_param_t), kTPM_EdgeAlignedPwm, 24000U, TPM_EDGE_CLOCK_SOURCE);
  TPM_StartTimer(TPM_EDGE_PERIPHERAL, kTPM_SystemClock);
}
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PV198 – One-chip Controllers, PWM / Dávid Danaj

Stepper motor demo
§Which mode can we use to get 4 signals as shown in the picture?
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PV198 – One-chip Controllers, PWM / Dávid Danaj

Homework
§Write 3 functions, that sets intensity for each color.
§Download HSV_RGB.h from study_materials/software
§All you have to do is periodically iterate over all colors by updating ‘H = (H + 1) % 360’

PV198 – One-chip Controllers, PWM / Dávid Danaj
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