AN1572

6/9

Doc ID 10604 Rev 2

Stop bit (ST)

If the oscillator has been determined to have stopped, it is recommended that users set and

then clear the oscillator stop bit (ST, bit 7 of address 1). This causes additional current to be

briefly injected into the oscillator to help get it running. We recommend using this kick-start

feature only when the oscillator is not running such as when the OF bit (oscillator fail status

bit) is set or when the device is being powered up for the first time.

If, upon power-up from backup mode, it is determined the device needs kick-starting, the

user should first clear the HT bit before setting the ST bit. Because the ST bit is part of the

seconds register, a write of the ST bit will result in the buffer/transfer registers being copied

to the counters. And if the HT bit is still set from power-down, the buffer/transfer registers

will contain the time of power-down. Thus kick-starting the device with HT set will result in

overwriting the date/time counters.

Furthermore, the user is reminded that the ST bit, being part of the seconds register, must

be packed with the seconds value. That is, the user must implement a read-modify-write

sequence on the seconds register when toggling the ST bit.