下面是官方时钟框图和datasheet例程及配套源代码，正常的思维是输入时钟除以分配即为LCD的时钟：32.768/2/18=910.22 ，但是官方是228；datasheet提供的计算方法和源代码也不一样当然他们的计算结果是一样的！

datasheet上还说LCDclk是RTCclk的一半但是这样算出来结果还是差一倍。

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void LCD_GLASS_Init(void)
{

  /*
    The LCD is configured as follow:
     - clock source = LSE (32.768 KHz)
     - Voltage source = Internal
     - Prescaler = 2
     - Divider = 18 (16 + 2)  
     - Mode = 1/4 Duty, 1/3 Bias
     - LCD frequency = (clock source * Duty) / (Prescaler * Divider)
                     = 228 Hz ==> Frame frequency = 57 Hz */

  /* Enable LCD clock */
  CLK_PeripheralClockConfig(CLK_Peripheral_LCD, ENABLE);
  CLK_RTCClockConfig(CLK_RTCCLKSource_LSE, CLK_RTCCLKDiv_1);

  /* Initialize the LCD */
  LCD_Init(LCD_Prescaler_2, LCD_Divider_18, LCD_Duty_1_4,
           LCD_Bias_1_3, LCD_VoltageSource_Internal);

  /* Mask register*/
  LCD_PortMaskConfig(LCD_PortMaskRegister_0, 0xFF);
  LCD_PortMaskConfig(LCD_PortMaskRegister_1, 0xFF);
  LCD_PortMaskConfig(LCD_PortMaskRegister_2, 0xFF);
  LCD_PortMaskConfig(LCD_PortMaskRegister_3, 0xFF);

  LCD_ContrastConfig(LCD_Contrast_Level_7);
  LCD_DeadTimeConfig(LCD_DeadTime_0);
  LCD_PulseOnDurationConfig(LCD_PulseOnDuration_1);

  LCD_Cmd(ENABLE); /*!< Enable LCD peripheral */
}