frequency e g 32 khz crystal oscillator 132 provides secondary timing for the ms 100 the primary functions of the low frequency timer are to keep track of real time even after the user has shut off the main power supply of the ms and to provide a u201c wake up u201d signal to bring the ms out of the low power sleep mode the low frequency timer 130 receives each frame pulse 124 from the high frequency timer 126 and calibrates itself against the frame pulse to compensate for drift in the frequency of the low frequency oscillator 132 this calibration process occurs over many frame pulses to reduce the effects of slow variations in the frequency of the low frequency oscillator 132 once calibrated the short term accuracy of the low frequency timer 130 is essentially as good as that of the high frequency timer 126 so that the low frequency oscillator 132 can be used to provide timing signals in the ms when the remaining circuitry including the high frequency timer 126 is in sleep mode during sleep mode the low frequency timer 130 determines when the receiver circuitry 102 must become active to receive the next paging signal from the base station and generates a wake up signal at the appropriate time fig2 is a detailed block diagram of the low frequency timer.