RTC timing issue

[BASAV]

HI!

I am using MC9S08DZ60 controller for my project and am configured RTC for 10 msec period interrupt generator. But am getting 12 msec. i.e 2 msec error. what could be the problem? clock input for RTC is 1-kHz internal low-power oscillator only  which is independent of MCG block. and the prescaler 8. tried with different configurations but error is persistent.

Here is my initialization code. 

#define RTC_MODULO      10 /*At 1KHz internal low power oscillator with prescaler 8 for 10ms interrupt */void bsp_rtc_init  ( void ){       bsp_io_rtcmod =  RTC_MODULO;     /*At 1KHz internal low power oscillator with prescaler %8 */        bsp_io_rtcsc = (BSP_IO_RTC_RTCLKS_1K_LPO | BSP_IO_RTC_RTIE | BSP_IO_RTC_RTCPS_DIV8);                                       /* Select clock,Setup prescalar, Enable interrupt. */}

[bigmac]

Hello,

The 1KHz internal low power oscillator can have a period anywhere within the limits 700 to 1300 microseconds, and this is likely to be quite dependent on supply voltage and operating temperature.  It is not a precision oscillator.  The measured 20 percent error is within the oscillator tolerance.

Regards,

Mac