We are trying to configure the RTC with External OSC. PCONP |= (1<<9); /* must be powered during configuration*/ /*--- Initialize registers ---*/ RTC_ILR = ILR_RTCALF | ILR_RTCCIF; /* Disable 32'768 interrupt */ RTC_AMR = 0; /* alarm mask register */ RTC_CIIR = 0; /* counter increment interrupt */ RTC_CCR |= CCR_CLKSRC; /* CCR_CLKSRC = 0x10 : external oscillator */ RTC_CISS = 0; But is not working can you help me send the configuration of external oscilltor RTC to LPC2300.