Skip to content

HardFOC driver

PCA9685 Driver

A C++20 driver for the NXP PCA9685 16-channel, 12-bit PWM controller. It sets the PWM frequency, drives each channel by duty cycle or by on/off tick, and controls sleep and the output stage, on any MCU with I2C.

Quickstart API guide Source on GitHub

The driver has no platform code. You give it a small class that brings an I2C bus up and reads and writes register bytes; it does the rest: the prescaler calculation, the sleep sequence the PRE_SCALE register needs, channel frames, retries and error flags.

16-channel, 12-bit PWM LED controller PCA9685 NXP Semiconductors
Outputs
16 channels, 12-bit (4096 steps) each, with a programmable on time and off time
PWM frequency
24 Hz to 1526 Hz, one frequency for all channels (25 MHz internal oscillator, or EXTCLK up to 50 MHz)
Host interface
I2C up to 1 MHz (Fast-mode Plus); 7-bit address 0x40 to 0x7F from pins A0 to A5
Output stage
Totem pole (25 mA sink, 10 mA source at 5 V) or open drain; OE pin, active low
Supply
2.3 V to 5.5 V, inputs and outputs 5.5 V tolerant; −40 °C to +85 °C
Package
TSSOP28, HVQFN28

Datasheet (Rev. 4)

What you get

  • One object per chip. PCA9685<YourBus> takes the bus and the 7-bit address; several chips share one bus. See API guide.
  • Frequency in hertz. SetPwmFreq() computes PRE_SCALE and runs the sleep / write / wake sequence the chip requires. See PWM timing.
  • Channels by duty or by tick. SetDuty(), SetPwm() with a phase offset, full on, full off and all channels at once. See API guide.
  • Errors you can inspect. Every call returns bool; a bitmask of Error flags says why. Register accesses retry with an optional delay. See API guide.
  • Zero-overhead portability. The port is a CRTP class with three methods: no virtual calls, no heap, no RTOS dependency. See Porting.
  • Tested without hardware. Host unit tests run the driver against a model of the chip's registers. See Testing and CI.

Where to go next

  • Quickstart

    Wire the chip, write the port, centre a servo in about 15 lines.

  • Hardware

    Pins, addresses, bus settings, output stage and power.

  • Architecture

    The three layers and what each one owns.

  • API guide

    Initialise, set the frequency, drive outputs and handle errors, task by task.

  • Porting

    Implement the I2C interface for your MCU.

  • API reference

    Every class and member, generated from the headers.