AN3060

RTC initialization

Doc ID 16253 Rev 2

21/23

Power-up from backup

Coming out of backup, the first thing to do is read the time. Prior to clearing the HT bit, the

RTC's buffer/transfer registers will contain the time of power down. If the duration of power

outage is needed by the application, the time of power down will be required. Otherwise,

this step can be skipped.

The next step is to clear the HT bit by writing it to 0. It is very important that the HT bit be

cleared prior to writing any of the timekeeping registers (addresses 0x00 to 0x07). Failure to

do so can resulting in corrupting the RTC counters.

If, at this point in the application flow, the present time is required, the time would be read.

With the HT bit clear, the present time will be returned by a read.

Upon servicing any interrupts from the RTC - e.g., alarm or OF - the flags register must be

cleared. Most of the flag bits clear upon reading, but the OF bit must be written to 0. Also,

the user should bear in mind that clearing the alarm flags (AF1, AF2) and oscillator fail flag

(OF) will clear the associated interrupt.

Figure 12.

Power-up from backup

Watchdog and timer

Lastly, power cycling always leaves the watchdog and timer disabled. If either is being used

by the application, they will need to be re-initialized.

Clear HT bit

Optional: Read time/date

(present time).

off_duration = present_time –

time_of-power-down

Clear any flags (read flags register)

Optional: Re-initialize watchdog.

Optional: Re-enable / Re-initialize

timer.

Optional: Read time/date

(time of power-down).

Power-up from backup

END

AM04730v1