Figure 6.3-4 Hxt Stop Protect Procedure; Figure 6.3-5 Systick Clock Control Block Diagram - Nuvoton ISD94124BYI Technical Reference Manual

The SysTick clock source can be from CPU clock or external reference clock, determined by
CLKSRC bit (SYST_CTRL[2]).
•
If CLKSRC = 1, CPU core clock is used for SysTick,
•
If CLKSRC = 0, SysTick clock source is from one of the 5 external reference clock, which
is chosen by STCLKSEL bits (CLK_CLKSEL0[5:3]), shown in Figure 6.3-5.

Figure 6.3-5 SysTick Clock Control Block Diagram

Sep 9, 2019
ISD94100 Series Technical Reference Manual
Set HXTFDEN To enable
HXT clock detector
NO
HXTFIF = 1?
YES
System clock source =
" HXT" or " PLL with
HXT" ?
YES
Switch system clock to
HIRC

Figure 6.3-4 HXT Stop Protect Procedure

HIRC
1/2
111
HCLK
1/2 011
HXT
1/2
010
LXT
001
HXT
000
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System clock keep
NO
original clock
STCLKSEL
(CLK_CLKSEL0[5:3])
STCLK
Rev1.09