RTC of ST10F276

[xiaomei]

Posted on October 11, 2007 at 08:24

RTC of ST10F276

[xiaomei]

Posted on October 08, 2007 at 06:55

Hi,

I wonder if anyone could help me on RTC of ST10F276. I want RTC to use low power 32kHz oscillator. The OSC bit (oscillator selection flag) in RTCCON register is read only. Can oscillator clock of RTC be selected. How to select oscillator clock (between main oscillator and low power 32kHz oscilator) if it can be selected. many thanks xz

[mirco23]

Posted on October 08, 2007 at 12:36

From the datasheet:

''At power on, and after Reset phase, if the presence of a 32 kHz oscillation on XTAL3 / XTAL4 pins is detected, then the RTC counter is driven by this low frequency reference clock: when Power Down mode is entered, the RTC can either be stopped or left running, and in both the cases the main oscillator is turned off, reducing the power consumption of the device to the minimum required to keep on running the RTC counter and relative reference oscillator. This is valid also if Stand-by mode is entered (switching off the main supply VDD), since both the RTC and the low power oscillator (32 kHz) are biased by the VSTBY. Vice versa, when at power on and after Reset, the 32 kHz is not present, the main oscillator drives the RTC counter, and since it is powered by the main power supply, it cannot be maintained running in Stand-by mode, while in Power Down mode the main oscillator is maintained running to provide the reference to the RTC module (if not disabled).'' The oscillator will be automatically selected. I don't know if you can choose the oscillator manually. [ This message was edited by: Mirco on 08-10-2007 16:07 ]

[najoua]

Posted on October 11, 2007 at 08:24

Hello xz,

What was said by Mirco is true: A 32 kHz crystal must be connected to the low power oscillator pins XTAL3 and XTAL4, in order to give a reference clock to the RTC module during power down mode. At power on, and after Reset phase, if the presence of a 32kHz oscillation on XTAL3 / XTAL4 pins is detected, then the RTC counter is driven by this low frequency reference clock. Regards, Najoua.