SN8P1700
8-bit micro-controller build-in 12-bit ADC
External RC Oscillator Frequency Measurement
There are two ways to get the Fosc frequency of external RC oscillator. One measures the XOUT output waveform.
Under external RC oscillator mode, the XOUT outputs the square waveform whose frequency is Fcpu. The other
measures the external RC frequency by instruction cycle (Fcpu). The external RC frequency is the Fcpu multiplied by 4.
We can get the Fosc frequency of external RC from the Fcpu frequency. The sub-routine to get Fcpu frequency of
external oscillator is as the following.
ꢃ
Example: Fcpu instruction cycle of external oscillator
B0BSET
P1M.0
; Set P1.0 to be output mode for outputting Fcpu toggle
signal.
@@:
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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