AN3060

RTC initialization

Doc ID 16253 Rev 2

19/23

First power-up

Since most of the peripheral and alarm functions are not enabled at power-up, there is little

urgency to initialize the part. The only item which might require immediate attention is the

squarewave function which powers-up running. Some applications may prefer to disable

this, or change its frequency.

The next thing the user should do is to write the HT bit to 0, then set the time and date. (For

other RTCs, at this point in the flow, if the ST bit is 1, it should be cleared to 0.)

If the application will be calibrated, this should be the next step.

Then the OF bit should be cleared (written to 0). Since power-up - since oscillator startup -

four seconds must have elapsed before this step is done. If calibration was performed, then

the time required to do that can be subtracted from the four seconds, and if calibration took

longer than that, then no additional waiting is required. The software should verify that the

OF bit remained cleared before progressing to the next step.

The next few items are optional. If the watchdog will be used, it can be started now,

assuming the software will soon get to the operational code which updates the watchdog.

Otherwise, the software should wait until the top of its main routine to start the watchdog.

If the timer or alarms will be used, the user might set them here, or again wait until the top of

the main routine. That will prevent any of these functions from timing out (interrupting) while

the processor is still running its initialization routine.