Safrianti, EryFeranitaKurniawan, Rudi2014-03-042014-03-042014-03-041693-9573wahyu sari yenihttp://repository.unri.ac.id/xmlui/handle/123456789/5761Real Time Clock (RTC) is an Integrated Circuit (IC) chip which has a function as a timepiece. RTC DS1307 has a register that can show seconds, minutes, hours, date, month and year. RTC has 64 locations Random Access Memory (RAM) consisting of 8 bytes for time data and control, and 56 byte RAM. Thus, by using microcontroller AT89S51 we could do data readings from RTC DS1307 and the results are displayed on a viewer Liquid Crystal Display (LCD) as a clock and calendar data. Microcontroller also provides functions to change clock, calendar and alarm time, these functions are accessible via 4x1 keypad interface. Reminder function performed by entering data into the memory AT89S51 time, then compare it with the readings from RTC DS1307. If the the result from DS1307 is the same with alarm time data, the microcontroller will generate an alarm signal for the speakers sounded the alarm. From the analysis conducted produced a digital calendar based on AT89S51 microcontroller that can be used as a time display and calendar viewer and an alarm as a reminder.enRTC DS1307Microcontroller AT89S51LCDCalendarUR-Scientific Work Lecturer