Adafruit_PWM_Servo_Driver.py 文件源码

def setPWMFreq(self, freq):
    "Sets the PWM frequency"
    prescaleval = 25000000.0    # 25MHz
    prescaleval /= 4096.0       # 12-bit
    prescaleval /= float(freq)
    prescaleval -= 1.0
    if (self.debug):
      print "Setting PWM frequency to %d Hz" % freq      
      print "Estimated pre-scale: %d" % prescaleval      
    prescale = math.floor(prescaleval + 0.5)
    if (self.debug):
      print "Final pre-scale: %d" % prescale      

    oldmode = self.i2c.readU8(self.__MODE1);
    newmode = (oldmode & 0x7F) | 0x10             # sleep
    self.i2c.write8(self.__MODE1, newmode)        # go to sleep
    self.i2c.write8(self.__PRESCALE, int(math.floor(prescale)))
    self.i2c.write8(self.__MODE1, oldmode)
    time.sleep(0.005)
    self.i2c.write8(self.__MODE1, oldmode | 0x80)