8.4 Clocking and Oscillator Control Registers
8.4.1 CLKSEL: Clock Select
Bit
7
6
5
4
3
2
1
0
Name
CLKRDY
CLKDIV
Reserved
CLKSL
Access
R
RW
R
RW
Reset
0
0x3
0
0x4
SFR Page = ALL; SFR Address: 0xA9
Bit
Name
Reset
Access
Description
7
CLKRDY
0
R
System Clock Divider Clock Ready Flag.
Value
Name
Description
0
NOT_SET
The selected clock divide setting has not been applied to the system clock.
1
SET
The selected clock divide setting has been applied to the system clock.
6:4
CLKDIV
0x3
RW
Clock Source Divider.
This field controls the divider applied to the clock source selected by CLKSL. The output of this divider is the system clock
(SYSCLK).
Value
Name
Description
0x0
SYSCLK_DIV_1
SYSCLK is equal to selected clock source divided by 1.
0x1
SYSCLK_DIV_2
SYSCLK is equal to selected clock source divided by 2.
0x2
SYSCLK_DIV_4
SYSCLK is equal to selected clock source divided by 4.
0x3
SYSCLK_DIV_8
SYSCLK is equal to selected clock source divided by 8.
0x4
SYSCLK_DIV_16
SYSCLK is equal to selected clock source divided by 16.
0x5
SYSCLK_DIV_32
SYSCLK is equal to selected clock source divided by 32.
0x6
SYSCLK_DIV_64
SYSCLK is equal to selected clock source divided by 64.
0x7
SYSCLK_DIV_128
SYSCLK is equal to selected clock source divided by 128.
3
Reserved
Must write reset value.
2:0
CLKSL
0x4
RW
Clock Source Select.
Selects the oscillator to be used as the undivided system clock source.
Value
Name
Description
0x0
HFOSC
Clock derived from the internal precision High-Frequency Oscillator.
0x1
EXTOSC
Clock derived from the External Oscillator circuit.
0x3
RTC
Clock derived from the RTC.
0x4
LPOSC
Clock derived from the Internal Low Power Oscillator.
There are no restrictions when switching between clock sources or divider values for this family.
EFM8SB2 Reference Manual
Clocking and Oscillators
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