Module pca9685 

NXP PCA9685 16-channel, 12-bit PWM controller.

The PCA9685 drives sixteen independent PWM outputs at one shared frequency, which is what makes it the usual way to run a bank of servos, dimmable LEDs, or the speed and direction inputs of motor drivers from a single I2C device. This module builds the values that program it: the prescaler that sets the output frequency, the address of each channel’s registers, and the 12-bit on/off word that sets a channel’s phase and duty, with the full-on and full-off encodings the datasheet defines.

It is pure logic: a caller writes the bytes to the device over whatever performs the I2C transfers.

Modules

mode1

Bit masks for the MODE1 register.

register

The PCA9685 register addresses.

Structs

Pwm

A channel’s PWM setting: when in the period it turns on and when it turns off.

Constants

CHANNELS

The number of PWM channels.

COUNTS

The number of counts in one PWM period (12-bit resolution).

INTERNAL_OSC_HZ

The frequency of the internal oscillator, 25 MHz.

MODE1_RESET

The power-on value of MODE1 (0x11): sleeping, responding to the All Call address.

PRE_SCALE_RESET

The power-on value of the PRE_SCALE register (0x1E), about 200 Hz at 25 MHz.

Functions

channel_register

Returns the address of a channel’s first register (its on-count low byte).

frequency_for_prescale

Computes the PWM frequency a PRE_SCALE value produces.

prescale_for_frequency

Computes the PRE_SCALE value for a desired PWM frequency.