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RA8804 CE
8.12. About access at the time of backup return and initial power supply
Because most of RTC registers are synchronized with the oscillation clock of the built-in crystal oscillator, the RTC does not
work normally without the integrated oscillator having stabilized. Please initialize the RTC at the time the power supply
voltage returns (VLF = 1) after the oscillation has stabilized (after oscillation start time tSTA).
If intending to access the RTC after the main supply voltage returns, please note following points:
1.
Please begin to read VLF-bit first.
If VLF-bit returns "1", please initialize all registers. Please perform initial setting only tSTA (oscillation start time),
2.
when the built-in oscillation is stable.
3.
Access is prohibited within 30 ms the supply voltage exceeds min. VCLK (clock supply voltage (VDD > 1.5 V).
If VLF-bit returns "0", access is possible without waiting time.
4.
5.
Before the internal crystal oscillator has stabilized (tSTA), no clock operation is possible and time is not counted.
VDD
Backup return and Initial power supply
Internal OSC
(Min.)
[V]
V
CLK
t
STA[s]
30[ms]
*) Please perform access to the data which clock counters depend on a
crystal oscillation for after tSTA time
Page - 36
An interface operation is possible
A clock operation is possible
ETM60E-02
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