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[PXCT-1269] - Nano R4 Documentation Update (PWM Resolution) #2621

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Sep 23, 2025
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[PXCT-1269] - Nano R4 Documentation Update (PWM Resolution) #2621

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Content update (PWM section)
canchebagur Sep 6, 2025
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Content review (Taddy's review)
canchebagur Sep 23, 2025
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21 changes: 18 additions & 3 deletions content/hardware/03.nano/boards/nano-r4/tutorials/01.user-manual/content.md
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Expand Up @@ -733,6 +733,8 @@ You can open the Arduino IDE's Serial Monitor (Tools > Serial Monitor) to see th

The Nano R4 board features multiple pins with PWM capability that can be used to generate analog-like output signals. PWM works by rapidly switching a digital output between `HIGH` and `LOW` states, where the ratio of `HIGH` time to the total period determines the effective analog voltage output.

***__PWM Compatibility Note__: The Nano R4 shares identical PWM capabilities with the UNO R4 Minima, as both boards use the same RA4M1 microcontroller. This includes the same default 8-bit resolution, maximum 16-bit resolution, and PWM frequency control features. Code written for PWM on the UNO R4 Minima will work identically on the Nano R4.***

The Nano R4 board provides PWM functionality on the following pins:

| **Arduino Pin** | **Microcontroller Pin** | **PWM Channel** | **Primary Function** |
Expand All @@ -744,21 +746,35 @@ The Nano R4 board provides PWM functionality on the following pins:
| `D10` | `P103` | Channel 2A | Digital I/O, SPI CS |
| `D11` | `P101` | Channel 5A | Digital I/O, SPI MOSI |

***__Important note:__ Pins `A4` and `A5` also have PWM capability but are primarily used for I²C communication (SDA and SCL respectively). The onboard LEDs (`LEDR`, `LEDG`, `LEDB`, `LED_BUILTIN`) also support PWM for brightness control.***
***__Important notes__: Pins `D3` and `D9` share the same PWM channel (`Channel 0B`) and cannot be used for PWM simultaneously. When using PWM on one of these pins, the other cannot output an independent PWM signal. Similarly, pins `D6`, `D3`, and `D9` all use timer `GPT0`, which means they will share the same PWM frequency setting. The onboard LEDs (`LEDR`, `LEDG`, `LEDB`, `LED_BUILTIN`) also support PWM for brightness control.***

The Nano R4's PWM offers the following technical specifications:

| **Specification** | **Value** | **Notes** |
|:------------------:|:----------------:|:------------------------------:|
| Default Resolution | 8-bit (0-255) | Standard Arduino compatibility |
| Maximum Resolution | 16-bit (0-65535) | Full precision control |

You can use PWM pins as analog output pins with the `analogWrite()` function:

```arduino
analogWrite(pin, value);
```

By default, the resolution is 8-bit (0 to 255). You can use analogWriteResolution() to change this, supporting up to 12-bit (0 to 4095) resolution:
**By default, the resolution is 8-bit (0 to 255)**. You can use the `analogWriteResolution()` resolution to change this, supporting up to 16-bit (0 to 65535) resolution:

```arduino
analogWriteResolution(resolution);
```

The Nano R4 supports the following PWM resolution options that you can configure based on your project's precision requirements:

- `analogWriteResolution(8)`: 8-bit resolution (0 to 255, **default resolution**)
- `analogWriteResolution(10)`: 10-bit resolution (0 to 1023)
- `analogWriteResolution(12)`: 12-bit resolution (0 to 4095)
- `analogWriteResolution(14)`: 14-bit resolution (0 to 16383)
- `analogWriteResolution(16)`: 16-bit resolution (0 to 65535, **maximum resolution**)

***The following PWM examples use the built-in orange user LED (`LED_BUILTIN`) of the Nano R4 board, which supports PWM for brightness control. This eliminates the need for external components and allows you to test PWM functionality immediately.***

The following example demonstrates how to control the brightness of the built-in orange user LED using PWM:
Expand Down Expand Up @@ -873,7 +889,6 @@ void loop() {
This high-resolution example creates a smooth sine wave pattern with the built-in LED brightness, demonstrating the precision available with a 12-bit PWM resolution. You should see a very smooth transition in the LED brightness following a sine wave pattern. Additionally, you can open the Arduino IDE's Serial Monitor (Tools > Serial Monitor) to see the angle and PWM value outputs that demonstrate the precise 12-bit control values being used.

![Arduino IDE Serial Monitor output for the high-resolution PWM example sketch](assets/pwm-3.png)

### Operational Amplifier (OPAMP)

The Nano R4 board features a built-in operational amplifier (OPAMP) that provides signal conditioning and amplification capabilities directly on the board. The OPAMP is connected to analog pins `A1`, `A2` and `A3`, allowing you to perform analog signal processing without requiring external amplifier circuits. This feature is particularly useful for sensor signal amplification, buffering and analog filtering applications.
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