SN8F2280 Series
USB 2.0 Full-Speed 8-Bit Micro-Controller
4.2.1 SYSTEM CLOCK MEASUREMENT
Under design period, the users can measure system clock speed by software instruction cycle (Fcpu). This way is
useful in RC mode.
Example: Fcpu instruction cycle of external oscillator.
B0BSET
P0M.0
; Set P0.0 to be output mode for outputting Fcpu toggle signal.
@@:
B0BSET
B0BCLR
JMP
P0.0
P0.0
@B
; Output Fcpu toggle signal in low-speed clock mode.
; Measure the Fcpu frequency by oscilloscope.
Note: Do not measure the RC frequency directly from XIN; the probe impendence will affect the RC
frequency.
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