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How to Interface I2C-RTC with AVR Development Board

AVR Development Board

The AVR Development Board is specifically designed to help students to master the required skills in the area of embedded systems. The kit is designed in such way that all the possible features of the microcontroller will be easily used by the students. The kit supports In-system programming (ISP) which is done through Parallel/Printer port.

ATMEL’s AVR (Atmega8535), AVR Development Kit is proposed to smooth the progress of developing and debugging of various designs encompassing of High speed 8-bit Microcontrollers.

I2C (Inter Integrated Circuit)

The I2C (Inter-IC) bus is a bi-directional two-wire serial bus that provides a communication link between integrated circuits (ICs).I2C is a synchronous protocol that allows a master device to initiate communication with a slave device. Data is exchanged between these devices.

RTC (Real Time Clock)

The DS1307 Serial Real-Time Clock is a low-power; full binary-coded decimal (BCD) clock/calendar plus 56 bytes of NV SRAM. Address and data are transferred serially via a 2-wire, bi-directional bus. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator.

Interfacing I2C - RTC

Fig. 1 shows how to interface the RTC with microcontroller through I2C. I2C is a Master-Slave protocol. I2C has a clock pulse along with the data. The master device controls the clock line, SCL. This line dictates the timing of all transfers on the I2C bus. No data will be transferred unless the clock is manipulated.

I2c bus supports many devices, each device is recognized by a unique address—whether it’s a micro-controller, LCD Driver, memory or keyboard interface and can operate as transmitter or receiver based on the functioning of the device. The controller designed controls the RTC ds1307 device through I2C protocol. The I2C Controller here acts as a master device and controls RTC ds1307 which acts as a slave. The read operation is accomplished by sending a set of control signals including the address and/or data bits. The control signals must be accompanied with proper clock signals.

Fig. 1 Interfacing I2C - RTC to Microcontroller


Interfacing I2C – RTC with AVR

We now want to read date & time by using I2C - RTC in AVR Development Board. Wiring up an I2C based RTC to the I2C port is relatively simple. The RTC also makes the software easier as it takes care of all calendar functions; accounting for leap years etc. The DS1307 (RTC) Real Time Clock IC (an I2C real time clock) is an 8 pin device using an I2C interface.

In AVR Development Kit, 2 nos. of RTC lines are controlled by I2C Enabled drivers. I2C Lines serial clock of CLK (PORTC.1), serial data of DATA (PORTC.0), connected to the I2C based serial RTC ds1307 IC. The date & times are read in AVR Development Kit by using these DATA & CLK I2C lines.

Pin Assignment with AVR







Turn ON RTC Pin of

CONFIG-II switch SW6.

Connect Serial cable between USART Section in the Board and PC.

Date and Time will be dis-played in HyperTerminal.

Seconds will be incrementing.




Circuit Diagram to Interface I2C–RTC with AVR

Source Code

The Interfacing I2C – RTC with AVR program is very simple and straight forward that read date & time in RTC by using I2C & the value is displayed in serial port. A delay is occurring in every single data read from RTC. The delay depends on compiler how it optimizes the loops as soon as you make changes in the options the delay changes.

C Program to interface I2C – RTC with AVR


Title : Program to read date & time from I2C - RTC


#include<mega8535.h> #include<delay.h> #include<stdio.h> #define TXIF UCSRA.5 #define BAUD 100000L //TWI frequency 100Khz #define FOSC 16000000L //Oscillator Frequency 16Mhz #define Prescale 4 //Prescalar set to 1:1 #define I2C_Baud ((FOSC / BAUD-16)/(2*Prescale)) #define SLA_W 0xd0 //EEPROM write and read #define SLA_R 0xd1 #define REP_START TWCR = 0xa4 //Following are TWI commands #define START TWCR = 0xa4 #define STOP TWCR = 0x94 #define CLR_TWINT TWCR = 0x84 #define Wait() while((TWCR & 0x80)==0) #define DATA TWDR #define USART_Baud 9600 #define BaudH ((unsigned int)(((FOSC/16/USART_Baud)-1) >> 8)) #define BaudL ((unsigned int)(((FOSC/16/USART_Baud)-1) & 0xFF)) unsigned char sec,min,hour,day,date,month,year; unsigned char data[7]={0x45,0x59,0x71,0x04,0x05,0x10,0x06}; unsigned char i=0; void DS1307Write(unsigned char, unsigned char); unsigned char DS1307Read(unsigned char); void I2c_init(void); void Serial_init(void); void main() { delay_ms(10); I2c_init(); Serial_init(); delay_ms(20); printf("\033[2J"); printf("DS1307 Demo Program: \r\n"); for(i=0;i<7;i++) DS1307Write(i,data[i]); //call write routines delay_ms(100); while(1) { sec = DS1307Read(0); // read second min = DS1307Read(1); // read minute hour = DS1307Read(2); // read hour day = DS1307Read(3); // read day date = DS1307Read(4); // read date month= DS1307Read(5); // read month year = DS1307Read(6); // read year printf("Time: %x : %x : %x ",(hour&0x1f),min,sec); printf("Date: %x / %x / %x \r", date, month, year); delay_ms(100); } } void DS1307Write(unsigned char addr, unsigned char data) { START; //send start pulse START=0xa4 Wait(); //wait untill the TWINT bit set,if TWINT bit //is ==1 process completed DATA = SLA_W; //send SLave Address + write bit CLR_TWINT; //clear TWINT bit by writing 1 into it Wait(); //wait untill the TWINT bit set DATA = addr; //Send the starting address where we are//going to write out data CLR_TWINT; Wait(); DATA=data; CLR_TWINT; Wait(); STOP; delay_ms(10); } unsigned char DS1307Read(unsigned char addr) { unsigned char RecDat=0; START; Wait(); DATA = SLA_W; CLR_TWINT; Wait(); DATA = addr; CLR_TWINT; Wait(); REP_START; Wait(); DATA = SLA_R; CLR_TWINT; Wait(); TWCR = 0xc4; CLR_TWINT; Wait(); RecDat=DATA; return RecDat; } void I2c_init() { TWCR = 0x04; TWSR = 0x01; TWBR = I2C_Baud; } void Serial_init(void) { UCSRA = 0x00; //Status Register UCSRB = 0x18; //Transmit Enable,Receive //enable,interrupts disabled UCSRC = 0x86; //8 databits,no parity,single stop UBRRH = BaudH; UBRRL = BaudL; } #define _ALTERNATE_PUTCHAR_ void putchar(unsigned char Data) { while(TXIF==0); UDR = Data; }

To compile the above C code you need the CodeVision AVR software. The software has it’s own IDE and built-in AVR gcc- Compiler. They must be properly installed and a project with correct settings must be created in order to compile the code. To compile the above code, the C file must be added to the project.

In CodeVision AVR software, you can develop or debug the project without any hardware setup. You must compile the code for generating HEX file. In debugging Mode, you want to check the port output without microcontroller Board.

The AVR Code Blaster software is used to download the hex file into your microcontroller through Parallel port.

Testing the I2C – RTC with AVR

Give +12V power supply to AVRDevelopment Board; the RTC Battery device is connected with the AVR Development Board. First check the entire Battery device fixed properly. A serial cable is connected between the microcontroller and PC.

In PC, open the Hyper Terminal for displaying the values from RTC.

Now, the Hyper Terminal shows the received data from RTC Battery through I2C.

If the Hyper Terminal is working but it is not reading any value from AVR Development Board, then you just check the configuration switch connections. Change the Battery & ds1307 device.

If you are not receiving any data in Hyper Terminal, then you just check the serial cable is working or not. Otherwise you just check the code with debugging mode in CodeVisionAVR.

General Information

  • For proper working use the components of exact values as shown in Circuit file. Wherever possible use new components.
  • Solder everything in a clean way. A major problem arises due to improper soldering, solder jumps and loose joints. Use the exact value crystal shown in schematic.
  • More instructions are available in following articles,

User Manual for ATMEGA Development Kit

How to create & Debug a Project in CodeVision AVR.