SH33F2801PSLASH032PR datasheet(52/407 Pages) SINOWEALTH

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SH33F2801

10.2.1

HSE Clock

High-speed external clock signal (HSE) is generated from two clock sources:

(1) External crystal/ceramic resonator: 4MHz - 12MHz

XTAL1

XTAL2

Crystal/

Ceramic

The 4~12Mz external oscillator (including crystal resonator and ceramic resonator) provides a more accurate clock for the

system. The HSERDY@RCC_CR bit in the clock control register is used to indicate if the high-speed external oscillator is

stable. At startup, the clock is not released until this bit is set to '1' by hardware. If an interrupt is allowed to be generated in the

clock interrupt register RCC_CIENR, a corresponding interrupt will be generated.

HSE crystal can be turned on and off by setting the HSEON@RCC_CR bit in the clock control register.

In order to reduce the distortion of the clock output and shorten the startup stabilizing time, the crystal/ceramic resonator

and the load capacitor must be as close as possible to the oscillator pins. The load capacitance value must be adjusted

according to the selected oscillator.

(2) External input clock: 4MHz – 12MHz

XTAL1

XTAL2

External Clock

In this mode, external clock must be provided. Its frequency could be as high as 12MHz. In this mode, the user must first fill

the external clock on XTAL1, and then turn on the HSEON bit, while XTAL2 must be left floating at this time. However, XTAL2

can be set to be used as a GPIO port by setting the OSCCFG@SYSCFG_SAFR bit to 10b.

Same as the external oscillator, the external clock also has a warm-up time and a Ready signal.

The external clock is also monitored by the CSM.

10.2.2

HSI Clock

The HSI clock signal is generated by internal 8MHz RC oscillator and can be used directly as the system clock or as PLL

input source. When acting as PLL input, it is recommended to turn on the PLL prescaler factor PLLXTPRE@RCC_CFGR,

which also means pre-division, is turned on.

HSI also has the following features:



After system reset, HSI is selected as the system clock.



HSI is always open after system power-on (whether or not the system clock uses HSI) and is turned off in stop mode.



Startup time of HSI RC oscillator is shorter than HSE crystal oscillator.



The HSI RC is calibrated to 0.2% (25°C) after production and does not exceed 1% over the full temperature range. At

system reset, the factory calibration value is loaded into HSICAL[7:0] bit of the clock control register. If the user's

application is based on different voltages or environment temperatures, this will affect the accuracy of the RC

oscillator. The HSI frequency can be further adjusted by HSITRIM[2:0] bit in the clock control register.

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