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RL78/G1A CHAPTER 22 SAFETY FUNCTIONS
22.3.7 Frequency detection function
The IEC60730 standard mandates checking that the oscillation frequency is correct.
By using the CPU/peripheral hardware clock frequency (f
CLK) and measuring the pulse width of the input signal to
channel 5 of the timer array unit 0 (TAU0), whether the proportional relationship between the two clock frequencies is
correct can be determined. Note that, however, if one or both clock operations are completely stopped, the proportional
relationship between the clocks cannot be determined.
<R>
<Clocks to be compared>
<1> CPU/peripheral hardware clock frequency (f
CLK):
• High-speed on-chip oscillator clock (f
IH)
• High-speed system clock (fMX)
<2> Input to channel 5 of the timer array unit
• Timer input to channel 5 (TI05)
• Low-speed on-chip oscillator clock (f
IL: 15 kHz (typ.))
• Subsystem clock (f
SUB)
Note
Figure 22-13. Configuration of Frequency Detection Function
TI05
f
CLK
High-speed on-chip
oscillator clock (f
IH
)
High-speed system
clock (f
MX
)
Subsystem clock
(f
SUB
)
Note
Low-speed on-chip
oscillator clock
(15 kHz (typ.))
Watchdog timer
(WDT)
<1>
<2>
f
IL
Channel 5 of timer
array unit 0
(TAU0)
SelectorSelector
If input pulse interval measurement results in an abnormal value, it can be concluded that the clock frequency is
abnormal.
For how to execute input pulse interval measurement, see 6.8.4 Operation as input pulse interval
measurement.
Note Can only be selected in the products incorporating the subsystem clock.
R01UH0305EJ0200 Rev.2.00 784
Jul 04, 2013