M451LG6AE Datasheet, PDF (162/219 Pages) List of Unclassifed Manufacturers – 32-bit Microcontroller

M451
Set HXTFDEN To enable
HXT clock detector
NO
HXTFIF = 1?
YES
System clock source =
“HXT” or “PLL with
HXT” ?
NO
System clock keep
original clock
YES
Switch system clock to
HIRC
Figure 6.3-4 HXT Stop Protect Procedure
The clock source of SysTick in Cortex^® -M4 core can use CPU clock or external clock
(SYST_CTRL[2]). If using external clock, the SysTick clock (STCLK) has 5 clock sources. The
clock source switch depends on the setting of the register STCLKSEL (CLK_CLKSEL0[5:3]). The
block diagram is shown in the following figure.
HIRC
1/2
HCLK
1/2
HXT
1/2
LXT
HXT
STCLKSEL
(CLK_CLKSEL0[5:3])
111
011
STCLK
010
001
000
Note: Before clock switching, both the pre-selected and newly selected clock sources must be turned on and stable.
Figure 6.3-5 SysTick Clock Control Block Diagram
6.3.4 Peripherals Clock
The peripherals clock has different clock source switch setting, which depends on the different
peripheral. Please refer to the CLK_CLKSEL1 and CLK_CLKSEL2 register description in 5.3.8.
Mar. 04, 2016
Page 162 of 219
Rev.2.05