Abstract: The DS1375 2-wire digital real-time clock (RTC) is a low-power, clock/calendar that can operate from a digital clock input at one of four frequencies: 32.768kHz, 8.192kHz, 60Hz, or 50Hz. This application note shows how to derive the 60Hz clock from the power line and use it as a clock for the DS1375. Power Line Frequency The 60Hz power line frequency is very carefully monitored. Throughout the day this frequency varies and tends to slow down during times of heavy use. Toward the end of the day the power company speeds up/slows down the frequency as needed so the total cycles in a given day is 5,184,000. In places that AC power is always available, a clock that uses a power line frequency of 60Hz will always be accurate over the long term. The Circuits The circuit in Solution 1 uses a transformer to step the 110 VAC power line to a safer 8 VAC (RMS). This circuit provides an inexpensive solution to extract the 60Hz clock from the power line. The 5.1V zener limits the AC to just the positive half of the cycle and suppresses anything more than 5.1V. The 1N4001 diode is then used to reference this to ground. If isolation is a concern, an optoisolator can be used (Solution 2) for additional cost. Configuring the DS1375 for 60Hz Clock Input To use an external 60Hz input, the DS1375 must be configured to accept this as a clock. This is done through the control register at address 0Eh, shown in Table 1. When ECLK is set to logic 1, the CLK input pin is enabled to clock the internal divider chain and advance the timekeeping registers. CLKSEL1 and CLKSEL0 determine how the CLK input pin is divided down to get the 1Hz reference clock for the timekeeping registers: Setting CLKSEL1 to 1 and CLKSEL0 to 0 configures the divider chain to accept a 60Hz clock. Table 1. Control register at address 0Eh Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ECLK CLKSEL1 CLKSEL0 RS2 RS1 INTCN A2IE A1IE Figure 1. Circuit to extract the 60Hz clock from the power line. Figure 2. Optoisolator solution for extracting a 60Hz clock. 의견을 보내주세요! 위 내용이 도움이 되셨나요? 여러분의 의견을 기다립니다 — Maxim은 보내주신 정정이나 제안사항을 반영하고 있습니다. 이 페이지를 평가하고 의견을 보내주십시오. 자동 업데이트 관심있는 분야의 애플리케이션 노트가 나올 때 자동으로 업데이트 받고 싶으세요? 그렇다면 EE-Mail™을 신청하십시오. 추가 정보   APP 1994: Apr 25, 2003 DS1375 알람기능이 내장된 2-Wire 디지털 입력 RTC 전체 데이터 시트 (PDF, 328kB) 무료 샘플   다운로드, PDF 형식 (100kB)  AN1994, AN 1994, APP1994, Appnote1994, Appnote 1994