ATMega644P TWI DS1307 MCP23017 LCD

In previous posts the ATMega644P TWI interface with the DS13017 RTC and MCP23017 GPIO expansion chip. Here I will put them altogethers. This TWI bus will drives the DS1307 RTC and the MCP23017 that controls a character LCD.

 

The master microcontroller read the RTC data from ds1307 and it will send to the MCP23017 based LCD. 

Source Code:

1. /*
2. * 10-i2c_ds1307_mcp23017_lcd.c
3. *
4. * Created: 2/7/2026 7:42:39 PM
5. * Author : Admin
6. */
7. 
   
8. #include <avr/io.h>
9. #include <util/delay.h>
10. #define F_CPU 16000000UL
11. 
    
12. void rtc_init(void){
13. char rtc[8]={0x30,0x00,0x17,0x07,0x31,0x01,0x26,1<<4};
14. for (char i=0;i<8;i++)
15. {
16. twi_start();
17. //D0 is DS1307 Write Address
18. twi_write(0xD0);
19. //Select Control Register
20. twi_write(i);
21. //Enable SQWE bit blinks at 1 Hz
22. twi_write(rtc[i]);
23. twi_stop();
24. _delay_ms(10);
25. }
26. }
27. 
    
28. char rtc[6], msg[16];
29. int main(void)
30. {
31. /* Replace with your application code */
32. _delay_ms(1000);
33. lcd_init();
34. lcd_text("ATMega644P TWI");
35. lcd_xy(1,2);
36. lcd_text("MCP23017 DS1307");
38. _delay_ms(10000);
39. lcd_clear();
40. lcd_command(0x0C);
41. while (1)
42. {
43. for(char i=0;i<7;i++){
44. /*Second Register*/
45. twi_start();
46. twi_write(0xD0);
47. /*Select Second register*/
48. twi_write(i);
49. twi_stop();
50. _delay_us(10);
52. twi_start();
53. twi_write(0xD1);
54. rtc[i]=twi_read(1);
55. twi_stop();
56. _delay_us(10);
57. }
59. lcd_xy(1,1);
60. sprintf(msg,"Time: %02X:%02X:%02X",rtc[2],rtc[1],rtc[0]);
61. lcd_text(msg);
62. lcd_xy(1,2);
63. sprintf(msg,"Date: %02X/%02X/20%02X",rtc[4],rtc[5],rtc[6]);
64. lcd_text(msg);
65. _delay_ms(500);
66. }
67. }
68. 
    

Circuit Simulation:

Circuit and Simulation

 

AVR Prototype Board

 

 

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Click here to download this example. 

For a full ATMega644P tutorials please visit this page.