Basics

The Real time clock DS1307 IC basically is stand alone time clock. Well, basically we can use a micrcontroller to keep time, but the value would go off as soon as it is powered off.

The RTC DS1307 is a handy solution to keep time all the way, when it is powered by a coin cell.

It is uses I²C (Inter-Integrated Circuit) protocol, referred to as I-squared-C, I-two-C, or IIC for communication with the micrcontroller.

Check the Basics of I2C here, if you are not familiar with it. For details of I2C in AVR, go through AVR Communication Protocols tutorial.

The first thing that the MCU sends to the slave (RTC) is the device ID. The device ID for DS1307, shown below. It also tells weather we want to write to or read from the RTC.

7 6 5 4 3 2 1 0
1 1 0 1 0 0 0 R/W
  • bit-0 is 0 than we Write to RTC
  • bit-0 is 1 we Read from RTC.

This is defined in the code as:

  1. #define C_Ds1307ReadMode_U8 0xD1u // DS1307 ID
  2. #define C_Ds1307WriteMode_U8 0xD0u // DS1307 ID

The RTC keeps the date and time arranged in it's memory as shown below:

ADDRESS FUNCTION RANGE
00h Seconds 00–59
01h Minutes 00–59
02h Hours 01-12/00-24
03h Day 01–07
04h Date 01–31
05h Month 01–12
06h Year 00–99
07h Control
08h to 3Fh RAM 00h–FFh

Write to the addresses above we can set the time, and once we set it, we can read it any time we need.


The address 0x07 is a control registered as described below:

7 6 5 4 3 2 1 0
OUT 0 0 SQWE 0 0 RS1 RS0

We write 0x00 to Control register to disable SQW-Out. We do not use any other bits from it, so you need not worry.

Initialize

Now we can initialize the RTC with the code below

  1. void RTC_Init(void)
  2. {
  3. I2C_Init(); // Initialize the I2c module.
  4. I2C_Start(); // Start I2C communication
  5.  
  6. I2C_Write(C_Ds1307WriteMode_U8); // Connect to DS1307 by sending its ID on I2c Bus
  7. I2C_Write(C_Ds1307ControlRegAddress_U8);// Select the Ds1307 ControlRegister to configure Ds1307
  8.  
  9. I2C_Write(0x00); // Write 0x00 to Control register to disable SQW-Out
  10.  
  11. I2C_Stop(); // Stop I2C communication after initializing DS1307
  12. }

Set Date and Time

  1. void RTC_SetDateTime(rtc_t *rtc)
  2. {
  3. I2C_Start(); // Start I2C communication
  4.  
  5. I2C_Write(C_Ds1307WriteMode_U8); // connect to DS1307 by sending its ID on I2c Bus
  6. I2C_Write(C_Ds1307SecondRegAddress_U8); // Request sec RAM address at 00H
  7.  
  8. I2C_Write(rtc->sec); // Write sec from RAM address 00H
  9. I2C_Write(rtc->min); // Write min from RAM address 01H
  10. I2C_Write(rtc->hour); // Write hour from RAM address 02H
  11. I2C_Write(rtc->weekDay); // Write weekDay on RAM address 03H
  12. I2C_Write(rtc->date); // Write date on RAM address 04H
  13. I2C_Write(rtc->month); // Write month on RAM address 05H
  14. I2C_Write(rtc->year); // Write year on RAM address 06h
  15.  
  16. I2C_Stop(); // Stop I2C communication after Setting the Date
  17. }

Note: The date and time read from Ds1307 will be of BCD format, like:

  • 0x12,0x39,0x26 for 12hr,39min and 26sec.
  • 0x15,0x08,0x47 for 15th day,8th month and 47th year

Get Date and Time

  1. void RTC_GetDateTime(rtc_t *rtc)
  2. {
  3. I2C_Start(); // Start I2C communication
  4.  
  5. I2C_Write(C_Ds1307WriteMode_U8); // connect to DS1307 by sending its ID on I2c Bus
  6. I2C_Write(C_Ds1307SecondRegAddress_U8); // Request Sec RAM address at 00H
  7.  
  8. I2C_Stop(); // Stop I2C communication after selecting Sec Register
  9.  
  10. I2C_Start(); // Start I2C communication
  11. I2C_Write(C_Ds1307ReadMode_U8); // connect to DS1307(Read mode) by sending its ID
  12.  
  13. rtc->sec = I2C_Read(1); // read second and return Positive ACK
  14. rtc->min = I2C_Read(1); // read minute and return Positive ACK
  15. rtc->hour= I2C_Read(1); // read hour and return Negative/No ACK
  16. rtc->weekDay = I2C_Read(1); // read weekDay and return Positive ACK
  17. rtc->date= I2C_Read(1); // read Date and return Positive ACK
  18. rtc->month=I2C_Read(1); // read Month and return Positive ACK
  19. rtc->year =I2C_Read(0); // read Year and return Negative/No ACK
  20.  
  21. I2C_Stop(); // Stop I2C communication after reading the Date
  22. }

Both the above functions use a simple structure shown below for easy access

  1. typedef struct
  2. {
  3. uint8_t sec;
  4. uint8_t min;
  5. uint8_t hour;
  6. uint8_t weekDay;
  7. uint8_t date;
  8. uint8_t month;
  9. uint8_t year;
  10. }rtc_t;

Example

Now, let's put together the all that we have discussed in a simple example to read and show the time on character LCD.

Hookup

Real Time Clock(DS1307) with AVR LCD RTC.png
Real Time Clock(DS1307) with AVR LCD bb.png

Code

#include "rtc.h"
#include "lcd.h"
int main()
{
rtc_t rtc;
/*Connect RS->PB0, RW->PB1, EN->PB2 and data bus to PORTB.4 to PORTB.7*/
LCD_SetUp(PB_0,PB_1,PB_2,P_NC,P_NC,P_NC,P_NC,PB_4,PB_5,PB_6,PB_7);
LCD_Init(2,16);
/*Connect SCL->PC0, SDA->PC1*/
RTC_Init();
rtc.hour = 0x10; // 10:40:20 am
rtc.min = 0x40;
rtc.sec = 0x00;
rtc.date = 0x01; //1st Jan 2016
rtc.month = 0x01;
rtc.year = 0x16;
rtc.weekDay = 5; // Friday: 5th day of week considering monday as first day.
/*##### Set the time and Date only once. Once the Time and Date is set, comment these lines
and reflash the code. Else the time will be set every time the controller is reset*/
RTC_SetDateTime(&rtc); // 10:40:20 am, 1st Jan 2016
/* Display the Time and Date continuously */
while(1)
{
RTC_GetDateTime(&rtc);
LCD_GoToLine(0);
LCD_Printf("time:%2x:%2x:%2x \nDate:%2x/%2x/%2x",(uint16_t)rtc.hour,(uint16_t)rtc.min,(uint16_t)rtc.sec,(uint16_t)rtc.date,(uint16_t)rtc.month,(uint16_t)rtc.year);
}
return (0);
}

Schematic

[1]

Schematic AVR Interfacing RTC.JPG

Real Time Clock(DS1307) with AVR.gif

Video Tutorial

For those of you, who would like to watch instead of read we have made a video with all the gyan.


Downloads

Download the complete project folder from the below link: https://github.com/ExploreEmbedded/ATmega32_ExploreUltraAvrDevKit/archive/master.zip


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