RA8900 SA / CE
Page - 32
ETM44E-01
8.11. About access at the time of backup return and Initial power supply
Because of most of RTC registers synchronize to an oscillation clock of a built-in crystal oscillator , RTC does not work
normally in a without inside oscillation. Please perform initial setting at the time of power supply voltage return from the state
that an oscillation stopped after progress in oscillation start time.
An access operation at the time of power supply voltage injection please be careful to the next points.
1) At the time of return from backup, please begin to read VLF-bit first.
2) When a reading result of VLF-bit is “1”, please initialize all registers.
Please perform initial setting after progress in the
oscillation start time when inside oscillation is stable.
3) Access is prohibited till 30ms passes after surpassing bottom value of clock supply voltage (VDD = 1.6V).
VDD
V
CLK
(
Min.
)
[
V
]
Internal OCS
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
4)
If a reading result of VLF-bit is “0”, user is accessible without waiting for oscillation start time.
5)
Even if an internal crystal oscillator does not oscillate, I2C interface of RA8900 can communicate with other devices.
