ISD94100 Series Technical Reference Manual
Sep 9, 2019
Page
144
of 928
Rev1.09
IS
D
9
410
0
S
ER
IE
S
T
E
C
HN
ICA
L
RE
F
E
RE
NCE
M
AN
U
AL
Set
HXTFDEN
To enable
HXT clock detector
HXTFIF
= 1?
System clock source =
“
HXT
”
or
“
PLL with
HXT
”
?
YES
System clock keep
original clock
NO
YES
Switch system clock to
HIRC
NO
Figure 6.3-4 HXT Stop Protect Procedure
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.
111
011
010
001
HXT
LXT
HXT
HCLK
STCLKSEL
(CLK_CLKSEL0[5:3])
STCLK
HIRC
000
1/2
1/2
1/2
Figure 6.3-5 SysTick Clock Control Block Diagram
