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PWM Control with CTIMER on the FRDM–MCXN947 Board

🎯 Objective:​

Learn how to configure and generate PWM signals using the CTIMER peripheral in MCUXpresso IDE on the FRDM–MCXN947 development board.

🔍 What are CTIMER and PWM?​

CTIMER (Counter/Timer) is a versatile on-chip peripheral found in NXP microcontrollers that can operate as a timer, counter, or PWM generator. PWM (Pulse-Width Modulation) is a technique to encode analog values using a digital signal by varying the duty cycle. It is widely used for motor control, LED dimming, and signal generation.

🖥️ Tools and Requirements​

  • IDE: MCUXpresso IDE (v11.5.0 or later)
  • Board: FRDM–MCXN947 development kit
  • Compiler: GNU Arm Embedded Toolchain (bundled with IDE)
  • Connectivity: USB cable for board programming and debugging

🧭 Workspace Overview​

When you open your project in MCUXpresso IDE:

  • Peripherals Perspective: Configure on-chip peripherals visually.
  • Problems View: Displays configuration errors and quick-fix suggestions.
  • Pins Perspective: Assign and route physical pins to peripheral functions.
  • Project Explorer: Browse source files and configuration.

✏️ Step-by-Step PWM Configuration

🧱 Main Steps​

  • Enable CTIMER Driver in Peripheral Drivers section.
  • Set Mode to PWM and configure clock prescaler.
  • Define PWM Channels and default duty cycles.
  • Route Pins in Pins Perspective or via quick-fix.
  • Generate Code and call the PWM update function in your application.

🔹 Step 1: Open Peripherals Perspective​

  1. In MCUXpresso IDE, click the Peripherals tab or switch via the perspective icon.
  2. Expand Peripheral Drivers (Device specific) and click + to add a new driver.

ERROR

🔹 Step 2: Enable CTIMER and Set Mode​

  1. Search for ctimer in the drivers list and press OK. ERROR

  2. In the CTIMER instance list, select the desired timer (e.g., CTIMER1). ERROR

  3. Under Mode, choose PWM. ERROR

🔹 Step 3: Resolve Clock Errors​

  • Go to the Problems tab (right corner).
  • Right-click any CTIMER_clock error (bulb icon) and apply the suggested fix to enable its clock. ERROR

🔹 Step 4: Configure Timer Frequency and Prescaler​

  1. In the CTIMER settings, set the Input Clock Frequency or Prescaler so that the timer base frequency supports your desired PWM frequency.

    • Explanation: The prescaler divides the bus clock to achieve a timer tick rate matching the PWM period requirements.

ERROR

  1. Start the timer in initialization code.

    • Explanation: The CTIMER counter must be running for PWM outputs to be generated. Check “Start the timer in initialization code” so the timer starts automatically during peripherals initialization—no manual CTIMER_StartTimer(...) call needed. ERROR

  2. Enter the PWM Frequency for the selected CTIMER channel. ERROR

🔹 Step 5: Add and Configure PWM Channels​

  1. In the PWM Channels section, click + to add a channel.
  2. Choose a channel number (1‒n, avoid channel 0) and set the Default Duty Cycle (applied at initialization before runtime updates). ERROR

🔹 Step 6: Route the PWM Pin​

  • Quick-Fix Method: In the Problems view, right-click the PWM pin assignment error and accept the suggested route. ERROR

  • Pins Perspective Method: Switch to Pins, search for ctimer<no>:match<pwm_channel_no>, enable the pin, and set Direction to Output (Routing Details - bottom section). ERROR

Tip: Verify the routed pin is available on a board header by consulting the FRDM–MCXN947 schematic.

🔹 Step 7: Generate Code​

  • After completing configuration, click Update Code to regenerate driver initialization based on your configuration. ERROR

🔹 Step 8: Using PWM in Application Code​

Call the generated driver function to update duty cycle at runtime:

CTIMER_UpdatePwmDutycycle(
    CTIMER<no>_PERIPHERAL,                      // e.g., CTIMER1_PERIPHERAL
    CTIMER<no>_PWM_PERIOD_CH,                   // the period channel defined in config
    CTIMER<no>_PWM_<pwm_channel_no>_CHANNEL,    // the channel index
    dutyPercent                                // new duty cycle in percent (integer)
);

⚙️ Advanced: Using Match Registers for Precise Duty Control​

When you need more precise control—for example, fractional duty cycles for servos or fine-grained LED brightness—you can calculate and write directly to the timer's match registers.

uint32_t periodTicks = CTIMER<no>_PERIPHERAL->MR[CTIMER<no>_PWM_PERIOD_CH];
uint32_t pulseTicks  = (uint32_t)((periodTicks * dutyPercent) / 100.0);
CTIMER<no>_PERIPHERAL->MR[<channelIndex>] = pulseTicks;

Explanation of Ticks and Duty Translation​

  • periodTicks: Total number of timer ticks for one full PWM period. It is read from the match register MR[CTIMER<no>_PWM_PERIOD_CH] which defines the period channel.

  • Timer Tick Duration: With a bus clock of, say, 48 MHz and a prescaler value P, each tick occurs every P / 48 000 000 seconds.

  • dutyPercent: Desired duty cycle as a percentage (0–100).

  • Calculating pulseTicks:

    1. Multiply periodTicks by dutyPercent / 100.0 to get the fractional portion of the period.
    2. Cast to uint32_t to obtain an integer tick count.

  • Writing to MR[channelIndex]: Setting this register tells the timer when (in ticks) to toggle the PWM output from high to low, achieving the specified duty cycle.

This method translates your percentage-based duty into concrete timer ticks, leveraging the full resolution of the CTIMER peripheral for precise PWM control.

🎉 Congratulations!

You have successfully configured and generated PWM signals on the FRDM–MCXN947 board using the CTIMER peripheral. Explore varying frequencies, multiple channels, and advanced timer features to build complex control applications.