Interfacing DS1307 RTC Chip with AVR Microcontroller

Real Time Clocks, as the name suggests are clock modules. They are available as integrated circuits (ICs) and manages timing like a clock. Some RTC ICs also manages date like a calendar. The main advantage is that they have a system of battery backup which keeps the clock/ca lender running even in case of power failure. A very small current is required for keeping the RTC alive. This in most case is provided by a miniature 3v lithium coin cell. So even if the embedded system with RTC is powered off the RTC module is up and running by the backup cell. This same technique is used in PC timing also. If you have opened your computer case you will notice a small coin cell in the mother board.

In this tutorial we will learn to use a very famous RTC IC named DS1307. The DS1307 is described in the datasheet as follows

The DS1307 is a low-power clock/calendar with 56 bytes of battery-backed SRAM. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The DS1307 operates as a slave device on the I2C bus.

So the aim of the project will be to access the DS1307 registers, read time

• Access the DS1307 registers i.e. read/write data to/from the DS1307 IC
• Format the read data and display in LCD
• Ability to get time from user and store it to DS1307. This provide means to setup the RTC module with correct time.

DS1307 Internal Registers

From software point of view the DS1307 is just a collection of some 8 bit registers. You can read these register to obtain the current time and date. You can also modify them to hold the correct time. After that the DS1307 keeps then updated with current date and time. The following registers are there.

ADDRESS	BIT7	BIT6	BIT5	BIT4	BIT3	BIT2	BIT1	BIT0	FUNCTION	RANGE
00H	CH	10 SECONDS			SECOND				SECOND	00-59
01H	0	10 MINUTES			MINUTES				MINUTES	00-59
02H	0	12	10HR	10HR	HOUR				HOUR	1-12+AM/PM OR 00-23
		24	am/pm
03H	0	0	0	0	0	DAY			DAY	01-07
04H	0	0	10 DATE		DATE				DATE	01-31
05H	0	0	0	10MONTH	MONTH				MONTH	01-12
06H	10 YEAR				YEAR				YEAR	00-99
07H	TO KEEP THINGS SIMPLE I HAVE SKIPPED THE CONTROL REGISTER THIS IS USED FOR SQUARE WAVE GENERATION ON PIN7
08-3FH									56 BYTE RAM	00h-FFh

The register uses BCD (Binary Coded Decimal) for storing the values. For example take register at address 01h, it stores the MINUTES. Say it is 37 minutes. Then it will be stored as follows.

Fig. : BCD Format in DS1307 Registers.

The DS1307.c and DS1307.h provide easy access to the registers. I have provided just two functions that allows you to read and write the DS1307 registers.

/***************************************************

Function To Read Internal Registers of DS1307
---------------------------------------------

address : Address of the register
data: value of register is copied to this.


Returns:
0= Failure
1= Success
***************************************************/

uint8_t DS1307Read(uint8_t address,uint8_t *data)




/***************************************************

Function To Write Internal Registers of DS1307
---------------------------------------------

address : Address of the register
data: value to write.


Returns:
0= Failure
1= Success
***************************************************/
uint8_t DS1307Write(uint8_t address,uint8_t data)

These functions depends on the I2C library. The I2C (Inter IC Communication) is a popular communication protocol between ICs. The DS1307 and our AVR ATmega8 communicates using the I2C bus. I will give more details on I2C in a separate tutorial.

A Simple RTC Module

The DS1307 require an 32.768KHz crystal, a 3v lithium battery and 2 pull up registers to function. So I will make a small PCB that will hold all these. The image of module is shown below. The module can be connected to development boards using female-female burg wires.

Fig. : A Simple DS1307 RTC Module.

 

Fig. :DS1307 RTC Module Circuit Diagram.

Once you have the RTC Module ready you can connect it with your favorite MCU like PIC or AVR or any other MCU. In this tutorial I will connect it with AVR ATmega8 MCU, I will also interface it with PIC MCUs latter on.

AVR ATmega8, DS1307 RTC Interface Example with LCD Module

To make a complete usable example we will connect a 16x2 LCD Module, and 3 push buttons. The detailed circuit diagram is given below.

Fig. :AVR ATmega8 RTC Interface Circuit Diagram.

avr-gcc software

The full software for the example is written in C language and compiled with avr-gcc. The whole software is very modular. Following software modules are used.

• LCD Interface modules for handling the display device. More detail is given on these pages.
  • LCD Interfacing library for Atmel AVR MCUs
  • LCD Interfacing library for Microchip PIC MCUs
• Low Level I2C Interface Library. This handles the data communication using the hardware I2C module present inside AVR/PIC MCUs.
  • For Atmel AVR MCUs (Yet to be written)
  • For PIC16 MCUs.(Yet to be written)
  • For PIC18 MCUs.(Yet to be written)
• DS1307 Module : This module built on top of above I2C module help in reading/writing data to and from the DS1307 chip. Functions are very simple and documented inside the .c and .h files itself.
• The main application module RTC.c is the application software that uses the above modules to communicate with both the LCD and DS1307 chip. It also manages the handling of UI (User Interface) by the help of 3 push buttons.

Fabrication Instructions

Assemble the circuits according to the circuit diagrams shown above. Burn the hex file (download link given at the end of article) to an ATmega8 using a suitable programmer. Set the fuse byte as follows LOW=21 HEX HIGH=D9 HEX . Apply power to the circuit and adjust the LCD Contrast Pot until the display is clear. The initial time should be shown as 00:00:00. Now press the "menu" key to enter the main menu. Use the LEFT and RIGHT Key to move between options and ENTER to select an item. The main menu has the following options.

• Set Time
• Set On Time (NOT IMPLEMENTED YET)
• Set Off Time (NOT IMPLEMENTED YET)
• Quit

Fig. : The Main Menu.

Go to the "Set Time" option, the following UI will be displayed.

Fig. : Setting the time.

Use the "Move Sel" key to move between Hour,Minute,Second,AM/PM, and <OK>. Use the "Increase"/"Decrease" buttons to adjust value. Finally go to <OK> and press any key. A message will be shown, "Main Time Set". The main menu will return. Select "Quit" from the main menu and the main screen showing the current time will be displayed. Now the RTC is setup, it will keep the time even if you switch off the circuit. Next the you power up the circuit it will still show the REAL time!

Fig. : DS1307 RTC Example Main Screen.

Downloads

• Full AVR Studio Project- To Learn More or Modify the software, load RTC.aps in AVR Studio.
• Precompiled HEX file for ATmega8

A Request From Readers

If you find this article useful or have any doubts or want to share your valuable suggestions, please leave a comment or two ! I would be glad to hear from you.

-The Author

Avinash Gupta

Videos

The ATmega8 DS1307 RTC Interface example in action.

17 Responses to “Interfacing DS1307 RTC Chip with AVR Microcontroller”

1. 1
   Kenneth Finnegan Says:
   

   I just finished my first project using the DS1307, and I appreciate your idea of building the complete module on perf board. I think I might go back and do that…

   There is a way around needing the pull-up resistors on the clock module (at least with an ATMEGA168): Set the SCL and SDA lines high, which enables pull-up resistors inside the controller. I only know how to do this in the Arduino environment, but I do know that it’s possible.

   I also used the SRAM, which was super convenient for when I wanted to be able to reset the atmega, but be able to pick up from where I left off.

   http://kennethfinnegan.blogspot.com/2009/10/arduino-temperature-logger.html

   October 23rd, 2009 at 11:36 am
2. 2
   foxit Says:
   

   I can not simulate this circuit in Proteus. It does not work.
   I don`t understand why. Please? help.

   October 23rd, 2009 at 2:57 pm
3. 3
   AVR Micro Says:
   

   This is an excellent article! Detailed description suitable also for beginners. I will not build this project but I enjoyed a lot reading it.

   October 23rd, 2009 at 8:12 pm
4. 4
   Anthony Says:
   

   Hi Avinash
   This is my favourite Chip (DS1307)
   I know it pretty Good

   I give a Lib for my friend
   for BCD->BIN
   *sec = ((*sec & 0xF0) >> 4)*10 + (*sec & 0×0F);
   *mnt = ((*mnt & 0xF0) >> 4)*10 + (*mnt & 0×0F);
   *hr = ((*hr & 0xF0) >> 4)*10 + (*hr & 0×0F);
   *day = ((*day & 0xF0) >> 4)*10 + (*day & 0×0F);
   *year = ((*year & 0xF0) >> 4)*10 + (*year & 0×0F);
   *date = ((*date & 0xF0) >> 4)*10 + (*date & 0×0F);
   *mn = ((*mn & 0xF0) >> 4)*10 + (*mn & 0×0F);

   for BIN->BCD
   _I2C_write(((sec/10)<<4) + (sec%10));
   _I2C_write(((min/10)<<4) + (min%10));
   _I2C_write(((hour/10)<<4) + (hour%10));

   ///////////////////////////////////////////////////////////

   ////Read Ram
   unsigned char rtc_read(unsigned char address_)
   {
   unsigned char data_;
   _i2c_start();
   _i2c_write(0xd0);
   _i2c_write(address_);
   _i2c_start();
   _i2c_write(0xd1);
   data=_i2c_read(0);
   _i2c_stop();
   return data_;
   }

   ///
   void rtc_write(unsigned char address,unsigned char data)
   {
   _i2c_start();
   _i2c_write(0xd0);
   _i2c_write(address);
   _i2c_write(data);
   _i2c_stop();
   }

   void rtc_init(unsigned char rs,unsigned char sqwe,unsigned char out)
   {
   rs&=3;
   if (sqwe) rs|=0×10;
   if (out) rs|=0×80;
   _i2c_start();
   _i2c_write(0xd0);
   _i2c_write(7);
   _i2c_write(rs);
   _i2c_stop();
   }

   void rtc_get_time(unsigned char *hour,unsigned char *min,unsigned char *sec)
   {
   _i2c_start();
   _i2c_write(0xd0);
   _i2c_write(0);
   _i2c_start();
   _i2c_write(0xd1);
   *sec=bcd2bin(_i2c_read(1));
   *min=bcd2bin(_i2c_read(1));
   *hour=bcd2bin(_i2c_read(0));
   _i2c_stop();
   }

   void rtc_set_time(unsigned char hour,unsigned char min,unsigned char sec)
   {
   _i2c_start();
   _i2c_write(0xd0);
   _i2c_write(0);
   _i2c_write(bin2bcd(sec));
   _i2c_write(bin2bcd(min));
   _i2c_write(bin2bcd(hour));
   _i2c_stop();
   }

   void rtc_get_date(unsigned char *date,unsigned char *month,unsigned char *year)
   {
   _i2c_start();
   _i2c_write(0xd0);
   _i2c_write(4);
   _i2c_start();
   _i2c_write(0xd1);
   *date=bcd2bin(_i2c_read(1));
   *month=bcd2bin(_i2c_read(1));
   *year=bcd2bin(_i2c_read(0));
   _i2c_stop();
   }

   void rtc_set_date(unsigned char date,unsigned char month,unsigned char year)
   {
   _i2c_start();
   _i2c_write(0xd0);
   _i2c_write(4);
   _i2c_write(bin2bcd(date));
   _i2c_write(bin2bcd(month));
   _i2c_write(bin2bcd(year));
   _i2c_stop();
   }

   October 23rd, 2009 at 8:27 pm
5. 5
   myway Says:
   

   anyone using SW I2C on other pins like scl and sda, i need simple function for i2c_write, i2c_start, i2c_read??
   thanks for help

   November 3rd, 2009 at 12:32 am
6. 6
   Praful Says:
   

   Dear Sir,
   I made a clock as per your design and used a hex file given by you but it just shows a cursor blinking on lcd and nothing else .
   I like this project and i want to do this but ………..
   Please help to solve this ……………
   Thanking You……………
   Praful
   09881303008

   November 17th, 2009 at 10:51 am
7. 7
   Avinash Says:
   

   @Praful

   When I published this project (or any other) I took GREAT CARE and try to give as much information as possible to SUCCESSFULLY make the project. I feel really pity at you that u could not make it May be some people are really too low on patience to ask at once that the thing is not working. The project is already a kind of like SPOON FEEDING a baby. I can’t do more than this.

   • Check the fuse bits
   • Check pull up resistor on SDA and SCL pins
   • If u don’t have enough knowledge please don’t try to be over smart and change/modify circuit and/or replace(with other value or equivalent) or remove componets
   November 17th, 2009 at 11:17 am
8. 8
   gaurav roy Says:
   

   dude.please complete the rf communication between microcontrollers.still waiting for that………….

   December 11th, 2009 at 2:21 am
9. 9
   Mathivanan Says:
   

   Great!!! Thanks…. Fully Explained ….Very nice Comments…

   January 15th, 2010 at 2:13 pm
10. 10
    kashif ali Says:
    

    quiet brief stuff, nicely explained..!!

    January 17th, 2010 at 6:40 pm
11. 11
    kunal Says:
    

    hi avinash, can you help me in interfacing atmega8 with PT2258. basicaly it’s a hometheatre project.
    thanks in advance.

    January 27th, 2010 at 3:49 pm
12. 12
    Ravi Kiran Says:
    

    Hi Avinash,

    I feel that there is a bug in the circuit that you have given.
    In the first image(in DS1307 Circuit), it is given that the SCL pin to be connected to the SDA pin of the MCU and SDA to SCL of the MCU. But the SCL pin of an I2C device should be connected to the SCL pin of any other I2C Device. I think this is a bug and please verify the same…
    Awaiting reply…..

    Thank You

    February 6th, 2010 at 12:31 pm
13. 13
    nazat shaikh Says:
    

    hi,
    I made a project only to read DS1307 after every 1sec and for that i took your code as a reference. I checked the hardware & everything is OK, but the RTC update the time only once.Please reply…..
    thank you

    February 12th, 2010 at 4:43 pm
14. 14
    alex Says:
    

    I made this circuit and code in proteus for simulate it, but I can not do it. I shall apreciate if someone can send me a file in proteus. and other question is why there are many code windows when I opened in avrStudio 4?, it can simulate or I need to add every code windows? please help me, sorry I’m novice, but I’ll try to do it. thanks a lot

    February 17th, 2010 at 8:53 am
15. 15
    Manas Paul Says:
    

    Dear Avinash Sir,
    This program is too good.This is my first AVR success program and LCD display program.Sir how I develop the 128×64 LCD display.Give the circuit diagram with program.I am also a customer of AVR kit.Thanks again.

    March 1st, 2010 at 10:42 pm
16. 16
    parag Says:
    

    hello sir,
    i am working on a project using PIC 16F877. can u help me for writing code for interfacing DS1307 with PIC using instructions only and not in c-language.
    please reply…
    thank u.

    March 5th, 2010 at 4:18 pm
17. 17
    Tifany Wiebusch Says:
    

    I go along with you actually, I believe! Might this become doable for you to have your blog translated directly into Russian? English is actually my own 2nd language.

    March 9th, 2010 at 7:38 pm

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