RX8804CE
Page - 38
ETM59E-05
8.11. 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:
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), when the
built-in oscillation is stable.
Access is prohibited about 30 ms, from the VCLK voltage. VCLK (clock supply voltage (V
DD
> 1.5 V).
If VLF-bit returns
“
0
”
, access is possible without waiting time.
Before the internal crystal oscillator has stabilized (tSTA), no clock operation is possible, and time is not counted.
VDD
V
CLK
Min.
Internal OSC
t
STA
s
An interface operation is possible
A clock operation is possible
Backup return and Initial power supply
30
ms
Please perform access to the data which clock counters
depend on a crystal oscillation for after tSTA time
Figure 26 Power ON and restore from backup sequence