RL78/G1P
CHAPTER 20 SAFETY FUNCTIONS
R01UH0895EJ0100 Rev.1.00
655
Nov 29, 2019
20.9 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 1 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.
Figure 20-13. Configuration of Frequency Detection Function
Watchdog timer
(WDT)
Channel 1 of timer
array unit 0
(TAU0)
X1
X2
TI01
f
IL
f
CLK
<1>
High-speed on-chip
oscillator (f
IH
)
X1 oscillator
(f
MX
)
Low-speed on-chip
oscillator
(15 kHz (TYP.))
Selector
Selector
<2>
<Operational overview>
Whether the clock frequency is correct or not can be judged by measuring the pulse interval under the following
conditions:
The internal high-speed oscillation clock (f
IH
) or the external X1 oscillation clock (f
MX
) 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 1 of timer array unit 0
(TAU0).
If pulse interval measurement results in an abnormal value, it can be concluded that the clock frequency is abnormal.
For how to execute pulse interval measurement, see
6.8.3 Operation as input pulse interval measurement
.