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专业名称：自动化

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2012年6月

Design of single chip real time clock and calendar based on

Abstract: This clock and calendar uses the AT89S52 microcontroller as the core for the control. Time Circuit which is constituted by Dallas's DS1302 real-time clock chip achieved a time and

date display, it increased functionality for the temperature display and the whole point timekeeping. This paper discusses the hardware circuit of the system, principle in detail , and gives the flow chart of the software design and the major source code. Keywords: microcontroller; real-time clock; Temperature measurement

1 Introduction

Clock and calendar-bedroom at home, schools, stations and more and more extensive use of plaza for people's lives, study, work great convenience. clock and calendar for the past need to re-adjust after power-off time and date, and time is a big error. Designed the system using real-time clock chip (DS1302) as a timer parts, the chip comes with an internal crystal oscillator, so that effectively guarantee the accuracy of the time and hang own internal battery power makes the situation will continue to update the time information . This design uses AT89S52 as the main controller, in order to improve the practicality of the circuit add temperature measurement circuit, timekeeping and alarm functions.

2 System hardware design

Schematic circuit shown in Figure 2:

System architecture diagram

2.1 Power Supply Circuit

In order to reduce circuit costs, the system power supply circuit by the transformer transformer, three-terminal integrated regulator (L7805> circuit 5V, has a simple, reliable, inexpensive and so on.

2.2 Host Controller

Host controller using ATMEL's latest MCU Products AT89S52. Apart from the single-chip microcomputer has a MCS-51 series single-chip all the benefits of things,also has 8KB of internal in-system programmable FLASH memory,free and low-power brown-out mode, greatly reducing the power circuit . In addition,also has a watchdog circuit,a reliable job for the circuit provides greater assurance.

2.3 digital tube display circuit

Show circuit with a high brightness,long life,low cost features such as the LED digital tube. Throughout the show circuit by the digital control and display LED drive circuit and decoding circuit. Because of the system to display the contents of more,a total of 16 digital tube, respectively,with eight shows year,month,day,four show time,show that 22 weeks,2 show the temperature. Controller in order to save resources,between the controller and displays add a decoding circuit 16 so that would have required the line of control into the circuit only 4 control lines,a great save system resources. The decoder by the decoder constitute both 3-8.

2.4 Real-time clock chip

This design uses the United States Dallas company DS1302, the chip can automatically generate century,year,month,day,hour,minute,second,such as time information. Century the use of internal registers with the software will be able to resolve the 'Millennium', the problem. The chip has its own internal battery-keng,external brown-out,the internal time information also be able to maintain for 10 years. Time for a single day record of 12 hours and there is a 24-hour mode. Time Table

Ways that also has two kinds of binary numbers,and the other with BCD code express. The chip with 128 bytes of internal RAM,one of 11 bytes used to store time information,4 bytes of memory