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M0A21/M0A23 Series
May 06, 2022
Page
195
of 746
Rev 1.02
M0
A21
/M
0
A
2
3
SE
RIES
TEC
H
NICAL
RE
FEREN
C
E
M
ANUAL
Clock Source Select Control Register 0 (CLK_CLKSEL0)
Register
Offset
R/W
Description
Reset Value
CLK_CLKSEL0
0x10
R/W
Clock Source Select Control Register 0
0x0000_003F
31
30
29
28
27
26
25
24
Reserved
23
22
21
20
19
18
17
16
Reserved
15
14
13
12
11
10
9
8
Reserved
7
6
5
4
3
2
1
0
Reserved
STCLKSEL
HCLKSEL
Bits Description
[31:6]
Reserved
Reserved.
[5:3]
STCLKSEL
Cortex
®
-M0 SysTick Clock Source Selection (Write Protect)
If SYST_CTRL[2]=0, SysTick uses listed clock source below.
000 = Clock source from HXT.
001 = Clock source from LXT.
010 = Clock source from HXT/2.
011 = Clock source from HCLK/2.
111 = Clock source from HIRC/2.
Other = Reserved.
Note 1:
If SysTick clock source is not from HCLK (i.e. SYST_CTRL[2] = 0), SysTick clock source must less
than or equal to HCLK/2.
Note 2:
This bit is write protected. Refer to the SYS_REGLCTL register.
[2:0]
HCLKSEL
HCLK Clock Source Selection (Write Protect)
Before clock switching, the related clock sources (both pre-select and new-select) must be turned on.
000 = Clock source from HXT.
001 = Clock source from LXT.
011 = Clock source from LIRC.
111= Clock source from HIRC.
Other = Reserved.
Note 1:
This bit is write protected. Refer to the SYS_REGLCTL register.
Note 2:
Reset by power on reset