text: import ustruct
  import pyb
  
  
  class PCA9685:
      def __init__(self, i2c, address=0x40):
          self.i2c = i2c
          self.address = address
          self.reset()
  
      def _write(self, address, value):
          self.i2c.writeto_mem(self.address, address, bytearray([value]))
  
      def _read(self, address):
          return self.i2c.readfrom_mem(self.address, address, 1)[0]
  
      def reset(self):
          self._write(0x00, 0x00) # Mode1
  
      def freq(self, freq=None):
          if freq is None:
              return int(25000000.0 / 4096 / (self._read(0xfe) - 0.5))
          prescale = int(25000000.0 / 4096.0 / freq + 0.5)
          old_mode = self._read(0x00) # Mode 1
          self._write(0x00, (old_mode & 0x7F) | 0x10) # Mode 1, sleep
          self._write(0xfe, prescale) # Prescale
          self._write(0x00, old_mode) # Mode 1
          pyb.udelay(5)
          self._write(0x00, old_mode | 0xa1) # Mode 1, autoincrement on
  
      def pwm(self, index, on=None, off=None):
          if on is None or off is None:
              data = self.i2c.readfrom_mem(self.address, 0x06 + 4 * index, 4)
              return ustruct.unpack('<HH', data)
          data = ustruct.pack('<HH', on, off)
          self.i2c.writeto_mem(self.address, 0x06 + 4 * index,  data)
  
      def duty(self, index, value=None, invert=False):
          if value is None:
              pwm = self.pwm(index)
              if pwm == (0, 4096):
                  value = 0
              elif pwm == (4096, 0):
                  value = 4095
              value = pwm[1]
              if invert:
                  value = 4095 - value
              return value
          if not 0 <= value <= 4095:
              raise ValueError("Out of range")
          if invert:
              value = 4095 - value
          if value == 0:
              self.pwm(index, 0, 4096)
          elif value == 4095:
              self.pwm(index, 4096, 0)
          else:
              self.pwm(index, 0, value)
  
  