SN8P1600
8-bit micro-controller
INTERNAL LOW-SPEED OSCILLATOR
The internal low-speed oscillator is built in the micro-controller. The low-speed clock source is a RC type oscillator
circuit. The low-speed clock can supplies clock for system clock and timer,.
ꢃ
ꢂ
Example: Stop internal low-speed oscillator.
B0BSET FCPUM0
; To stop external high-speed oscillator and internal low-speed
; oscillator called power down mode (sleep mode).
Note: The internal low-speed clock can’t be turned off individually. It is controlled by CPUM0 bit of OSCM
register.
The low-speed oscillator uses RC type oscillator circuit. The frequency is affected by the voltage and temperature of
the system. In common condition, the frequency of the RC oscillator is about 16KHz at 3V and 32KHz at 5V. The
relative between the RC frequency and voltage is as the following figure.
Internal RC vs. VDD
40
38.678
35.343
35
32.008
30
28.673
25.338
25
22.003
20
18.668
15.333
15
11.998
10
8.663
7.329
5
0
1.80 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50
VDD (Volts)
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Example: Measure the internal RC frequency by instruction cycle (Fcpu). The internal RC frequency is the
Fcpu multiplied by 4. We can get the Fosc frequency of internal RC from the Fcpu frequency.
B0BSET
B0BSET
P1M.0
; Set P1.0 to be output mode for outputting Fcpu toggle signal.
; Switch the system clock to internal low-speed clock mode.
FCLKMD
@@:
B0BSET
B0BCLR
JMP
P1.0
P1.0
@B
; Output Fcpu toggle signal in low-speed clock mode.
; Measure the Fcpu frequency by oscilloscope.
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