Nations N32G45 Series, User Manual

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104 / 838
Nations Technologies Inc.
Tel
：
+86-755-86309900
Email
：
info@nationstech.com
Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China

HSE user external clock
To reduce distortion of the clock output and shorten the start-up Stablize time, the crystal/ceramic resonator and
load capacitor must be placed as close as possible to the oscillator pins. The load capacitance value must be
adjusted according to the chosen oscillator.
Figure 6-3 HSE/LSE clock source
External clock source (HSE bypass)
In this mode, an external clock source must be provided. Its frequency can be up to 32MHz. Users can select this
mode by setting the RCC_CTRL.HSEBP and RCC_CTRL.HSEEN bits. The external clock signal(50% duty cycle
square, sine or triangle wave) must be connected to the OSC_IN pin while the OSC_OUT pin must be left floating
(Hi-Z). See Figure 6-3.
External crystal/ceramic resonator (HSE crystal)
The 4 to 32 MHz external oscillator has the advantage of producing a more accurate master clock for the system. The
associated hardware configuration is shown in See Figure 6-3. For more details, please refer to the electrical
characteristics section of the datasheet.
The RCC_CTRL.HSERDF bit indicates whether the high-speed external oscillator is stable or not. At startup, the
clock is not released until this bit is set by hardware. An interrupt can be generated if enabled in the Clock Interrupt
Register (RCC_CLKINT).
HSE clock can be switched on and off by setting the RCC_CTRL.HSEEN bit.
6.2.3 HSI clock
The HSI (High Speed Internal) clock signal is generated by an internal 8MHz RC oscillator and can be used directly
as system clock or as PLL input after dividing by 2. The HSI RC oscillator can provide a clock source without any
external devices. It also has a shorter startup time than the HSE crystal oscillator. However, its frequency is less
accurate even with calibration.
The HSI clock frequency of each chip has been calibrated to 1% (25°C) before leaving the factory. After the system
reset, the factory calibration value is loaded into the RCC_CTRL.HSICAL[7:0] bits.
If the user application is subject to voltage or temperature variations, this may affect the accuracy of the RC oscillator.
External Clock
OSC_OUT
(HiZ)
External Clock Source
OSC_OUT OSC_IN
Crystal
C1 C2
Crystal/Ceramic Resonators