RL78/G13 CHAPTER 22 SAFETY FUNCTIONS
R01UH0146EJ0100 Rev.1.00 914
Sep 22, 2011
22.3.7 Frequency detection function
The IEC60730 standard mandates checking that the oscillation frequency is correct.
The frequency detection function can detect whether the clock is operating on an abnormal frequency by comparing the
internal high-speed oscillation clock or external X1 oscillation clock with the internal low-speed oscillation clock (15 kHz).
Figure 22-12. Configuration of Frequency Detection Function
<Operational overview>
Whether the clock frequency is correct or not can be judged by measuring the pulse width under the following
conditions:
• The internal high-speed oscillation clock (f
IH) or the external X1 oscillation clock (fMX) is selected as the
CPU/peripheral hardware clock (f
CLK).
• The internal low-speed oscillation clock (f
IL: 15 kHz) is selected as the timer input for channel 5 of timer array unit 0
(TAU0).
If pulse width measurement results in an abnormal value, it can be concluded that the clock frequency is abnormal.
For how to execute pulse width measurement, see 6.7.4 Operation as input pulse interval measurement.
Timer array unit 0
(TAU0)
TI05
Watchdog timer
(WDT)
fCLK
Selector
f
IL
X1
X2
Selector
Low-speed on-chip
oscillator
(15 kHz)
X1 oscillator
(f
MX)
High-speed on-chip
ossiratopr (f
IH
)
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