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

 

 

This PCB was offered by PCBWay (pcbway.com).

I have been using PCBWay for many years now. PCBWay fabricate PCBs at low cost, fast processing time for only 24 hours, and fast delivery time using any carrier options. This double side 10cmx10cm can be fabricate at only 5USD for 5 to 10pcs by PCBWay. It's a standard PCB with silk screen and solder mask.

10 PCBs for only 5USD

 

For different size of PCB we can instantly quote on PCBWay website using a zip PCB Gerber file without account.

PCBWay Instant Quote

 

Click here to download this example. 

For a full ATMega644P tutorials please visit this page.

ATMega644P TWI MCP23017 Character LCD

The HD44780 based character LCD can be controlled by a micro-controller, digital circuit, an I/O expansion chip or event by hands. In this example I use an output port of the MCP23017 to control a 16x2 LCD in one direction (write only) in 4-bit data transfer mode.

The LCD connect to GPIOB (output register OLATB). That's,

• LCD RS (GPB0)
• LCD R/W (GPB1)
• LCD EN(GPB2)
• D4:D7(GPB4:GPB7)

Source Code: "main.c"

1. /*
2. * 10-i2c_mcp23017_1602.c
3. *
4. * Created: 2/5/2026 8:03:45 PM
5. * Author : Admin
6. */
7. 
   
8. #include<stdio.h>
9. #include <avr/io.h>
10. #include <util/delay.h>
11. #define F_CPU 16000000UL
12. 
    
13. //IOCON.BANK=0
14. enum BANK0{
15. IODIRA=0,IODIRB,IPOLA,IPOLB,GPINTENA,GPINTENB,DEFVALA,
16. DEFVALB,INTCONA,INTCONB,IOCON1,IOCON2,GPPUA,GPPUB,
17. INTFA,INTFB,INTCAPA,INTCAPB,GPIOA,GPIOB,OLATA,OLATB
18. };
19. 
    
20. const char RS=0,RW=1,EN=2;
21. char BLK_ON=0;
22. 
    
23. void lcd_command(uint8_t temp){
24. uint8_t command,led;
25. command=temp&0xF0;
26. if(BLK_ON==1) led=0x08;
27. else led=0;
28. mcp23017_write(OLATB,command|led|(1<<EN));
29. _delay_us(10);
30. mcp23017_write(OLATB,command|led);
31. _delay_us(25);
33. command=temp<<4;
34. mcp23017_write(OLATB,command|led|(1<<EN));
35. _delay_us(10);
36. mcp23017_write(OLATB,command|led);
37. _delay_us(25);
38. }
39. 
    
40. void lcd_data(uint8_t temp){
41. uint8_t data,led;
42. data=temp&0xF0;
43. if(BLK_ON==1) led=0x08;
44. else led=0;
45. mcp23017_write(OLATB,data|led|(1<<EN)|(1<<RS));
46. _delay_us(10);
47. mcp23017_write(OLATB,data|led|(1<<RS));
48. _delay_us(25);
50. data=temp<<4;
51. mcp23017_write(OLATB,data|led|(1<<EN)|(1<<RS));
52. _delay_us(10);
53. mcp23017_write(OLATB,data|led|(1<<RS));
54. _delay_us(25);
55. }
56. 
    
57. void lcd_xy(uint8_t x, uint8_t y){
58. uint8_t cursor[]={0x80,0xC0};
59. lcd_command(cursor[y-1]+x-1);
60. }
61. 
    
62. void lcd_text(uint8_t *text){
63. while(*text) lcd_data(*text++);
64. }
65. 
    
66. void lcd_clear(void){
67. lcd_command(0x01);
68. _delay_ms(5);
69. }
70. 
    
71. void lcd_init(void){
72. BLK_ON=1;
73. mcp23017_write(IODIRB,0x00);
74. lcd_command(0x33);
75. _delay_us(10);
76. lcd_command(0x32);
77. _delay_us(10);
78. lcd_command(0x28);
79. _delay_us(10);
80. lcd_command(0x0F);
81. _delay_us(10);
82. lcd_command(0x01);
83. _delay_ms(5);
84. lcd_command(0x06);
85. _delay_us(10);
86. }
87. 
    
88. int main(void)
89. {
90. /* Replace with your application code */
91. lcd_init();
92. lcd_text("MCP23017 TWI");
93. lcd_xy(1,2);
94. lcd_text("MCP23017 LCD");
95. 
    
96. _delay_ms(10000);
97. lcd_clear();
98. lcd_command(0x0C);
101. lcd_text("Counter Value:");
102. long counter=0;
103. char msg[10];
104. while (1)
105. {
106. sprintf(msg,"%ld",counter);
107. lcd_xy(1,2); lcd_text(msg);
108. counter++;
109. _delay_ms(500);
110. }
111. }
112. 
     

Source Code: "mcp23017.c"

1. /*
2. * mcp23017.c
3. *
4. * Created: 2/5/2026 8:06:38 PM
5. * Author: Admin
6. */
7. 
   
8. const char MCP23017_W=0x40;
9. const char MCP23017_R=0x41;
10. 
    
11. //IOCON.BANK=0
12. /*
13. enum BANK0{
14. IODIRA=0,IODIRB,IPOLA,IPOLB,GPINTENA,GPINTENB,DEFVALA,
15. DEFVALB,INTCONA,INTCONB,IOCON1,IOCON2,GPPUA,GPPUB,
16. INTFA,INTFB,INTCAPA,INTCAPB,GPIOA,GPIOB,OLATA,OLATB
17. };
18. */
19. 
    
20. 
    
21. void mcp23017_write(char address,char data){
22. twi_start();
23. /*Select the write address*/
24. twi_write(MCP23017_W);
25. /*Select a register address*/
26. twi_write(address);
27. /*Send configuration data*/
28. twi_write(data);
29. twi_stop();
30. }
31. 
    
32. unsigned char mcp23017_read(char address){
33. /*Select a specific address*/
34. twi_start();
35. twi_write(MCP23017_W);
36. twi_write(address);
37. twi_stop();
38. /*Read data from the given address*/
39. twi_start();
40. twi_write(MCP23017_R);
41. unsigned char i2cData=twi_read(1);
42. twi_stop();
43. return i2cData;
44. }

Source Code: "twi.c" 

1. /*
2. * twi.c
3. *
4. * Created: 2/4/2026 10:22:02 AM
5. * Author: Admin
6. */
7. 
   
8. #include <avr/io.h>
9. #include <util/delay.h>
10. #define F_CPU 16000000UL
11. 
    
12. 
    
13. void twi_init(void){
14. TWSR|=0x00; //Prescaler Selection Bit
15. TWBR=0x0F; //Baud Rate Generator
16. TWCR=(1<<TWEN); //Enable The TWI Module
17. PORTC|=(1<<0);
18. PORTC|=(1<<1);
19. }
20. 
    
21. void twi_start(void){
22. TWCR=(1<<TWINT)|(1<<TWSTA)|(1<<TWEN);
23. while((TWCR&(1<<TWINT))==0);
24. }
25. 
    
26. void twi_write(unsigned char data){
27. TWDR=data;
28. TWCR=(1<<TWINT)|(1<<TWEN);
29. while((TWCR&(1<<TWINT))==0);
30. }
31. 
    
32. unsigned char twi_read(char ACK){
33. if(ACK==0)
34. TWCR=(1<<TWINT)|(1<<TWEN)|(1<<TWEA);
35. else
36. TWCR=(1<<TWINT)|(1<<TWEN);
37. while((TWCR&(1<<TWINT))==0);
38. return TWDR;
39. }
40. 
    
41. void twi_stop(){
42. TWCR=(1<<TWINT)|(1<<TWEN)|(1<<TWSTO);
43. _delay_us(10);
44. }

Schematic:

 

AVR Prototype Board: 

AVR Experiment Board

For PIC micro-controller using PIC16F887 is a good choice.

This PCB was offered by PCBWay (pcbway.com).

I have been using PCBWay for many years now. PCBWay fabricate PCBs at low cost, fast processing time for only 24 hours, and fast delivery time using any carrier options. This double side 10cmx10cm can be fabricate at only 5USD for 5 to 10pcs by PCBWay. It's a standard PCB with silk screen and solder mask.

10 PCBs for only 5USD

 

For different size of PCB we can instantly quote on PCBWay website using a zip PCB Gerber file without account.

PCBWay Instant Quote

 

There is one port left, GPIOA. So I added a 4x4 matrix keypad at GPIOA. The result of keypad scanning will show on the LCD.

Source Code:

 

1. /*
2. * 10-i2c_mcp23017_1602_kb.c
3. *
4. * Created: 2/5/2026 10:32:40 PM
5. * Author : Admin
6. */
7. 
   
8. #include<stdio.h>
9. #include <avr/io.h>
10. #include <util/delay.h>
11. #define F_CPU 16000000UL
12. 
    
13. //IOCON.BANK=0
14. enum BANK0{
15. IODIRA=0,IODIRB,IPOLA,IPOLB,GPINTENA,GPINTENB,DEFVALA,
16. DEFVALB,INTCONA,INTCONB,IOCON1,IOCON2,GPPUA,GPPUB,
17. INTFA,INTFB,INTCAPA,INTCAPB,GPIOA,GPIOB,OLATA,OLATB
18. };
19. 
    
20. const char RS=0,RW=1,EN=2;
21. char BLK_ON=0;
22. 
    
23. const char key_16[4][4]={'1','2','3','A',
24. '4','5','6','B',
25. '7','8','9','C',
26. '*','0','#','D'};
27. 
    
28. char keyScan(void){
29. char data=0,temp,key;
30. for(char i=0;i<4;i++){
31. data=0xFF;
32. data&=~(1<<i);
33. mcp23017_write(OLATA,data);
34. _delay_ms(5);
35. data=mcp23017_read(GPIOA);
36. data&=0xF0;
37. if((data&0x10)==0) {temp=key_16[i][0]; break;}
38. else if((data&0x20)==0){temp=key_16[i][1]; break;}
39. else if((data&0x40)==0){temp=key_16[i][2]; break;}
40. else if((data&0x80)==0){temp=key_16[i][3]; break;}
41. else temp=0;
42. _delay_ms(10);
43. }
44. return temp;
45. }
46. void lcd_command(uint8_t temp){
47. uint8_t command,led;
48. command=temp&0xF0;
49. if(BLK_ON==1) led=0x08;
50. else led=0;
51. mcp23017_write(OLATB,command|led|(1<<EN));
52. _delay_us(10);
53. mcp23017_write(OLATB,command|led);
54. _delay_us(25);
56. command=temp<<4;
57. mcp23017_write(OLATB,command|led|(1<<EN));
58. _delay_us(10);
59. mcp23017_write(OLATB,command|led);
60. _delay_us(25);
61. }
62. 
    
63. void lcd_data(uint8_t temp){
64. uint8_t data,led;
65. data=temp&0xF0;
66. if(BLK_ON==1) led=0x08;
67. else led=0;
68. mcp23017_write(OLATB,data|led|(1<<EN)|(1<<RS));
69. _delay_us(10);
70. mcp23017_write(OLATB,data|led|(1<<RS));
71. _delay_us(25);
73. data=temp<<4;
74. mcp23017_write(OLATB,data|led|(1<<EN)|(1<<RS));
75. _delay_us(10);
76. mcp23017_write(OLATB,data|led|(1<<RS));
77. _delay_us(25);
78. }
79. 
    
80. void lcd_xy(uint8_t x, uint8_t y){
81. uint8_t cursor[]={0x80,0xC0};
82. lcd_command(cursor[y-1]+x-1);
83. }
84. 
    
85. void lcd_text(uint8_t *text){
86. while(*text) lcd_data(*text++);
87. }
88. 
    
89. void lcd_clear(void){
90. lcd_command(0x01);
91. _delay_ms(5);
92. }
93. 
    
94. void lcd_init(void){
95. BLK_ON=1;
96. mcp23017_write(IODIRB,0x00);
97. lcd_command(0x33);
98. _delay_us(10);
99. lcd_command(0x32);
100. _delay_us(10);
101. lcd_command(0x28);
102. _delay_us(10);
103. lcd_command(0x0F);
104. _delay_us(10);
105. lcd_command(0x01);
106. _delay_ms(5);
107. lcd_command(0x06);
108. _delay_us(10);
109. }
110. 
     
111. int main(void)
112. {
113. /* Replace with your application code */
114. lcd_init();
115. lcd_text("MCP23017 TWI");
116. lcd_xy(1,2);
117. lcd_text("LCD and Key Pad");
118. 
     
119. _delay_ms(10000);
120. lcd_clear();
122. //Key Pad Init
123. mcp23017_write(IODIRA,0xF0);
124. mcp23017_write(GPPUA,0xF0);
125. char temp,charCount=0,newLine=0,line=1;
126. while (1)
127. {
128. temp=keyScan();
129. if(temp!=0){
130. lcd_data(temp);
131. charCount++;
132. _delay_ms(500);
133. }
134. if(charCount>16){
135. newLine=1;
136. charCount=0;
137. line+=1;
138. }
139. if(newLine){
140. newLine=0;
141. if(line==2) lcd_xy(1,2);
142. else{
143. lcd_xy(1,1);
144. lcd_command(0x01);
145. _delay_ms(5);
146. line=1;
148. }
149. }
150. }
151. }
152. 
     
153. 
     

Program Simulation:

Program Simulation

AVR Prototype Board: 

 

 

 

Click here to download this example. 

For a full ATMega644P tutorials please visit this page. 

ATMega644P TWI MCP23017 LCD Keypad

The MCP23017 can be use as input or output depends on its register configurations. A 4x4 matrix keypad requires only one 8-bit I/O port of its master controller. So I use one general I/O port the GPA of the MCP23017 to scan a 4x4 matrix keypad. Founded key will show on a16x2 character LCD.

The LCD is already place on board. The MCP23017 interfaces to the ATMega644P using only two TWI wires. But it need to place and wire on a breadboard module with the keypad.

 

I use a remembrance 4x4 keypad module that's ready to connect to GPA.

• "main.c"

1. /*
2. * 10-i2c_mcp23017_keypad.c
3. *
4. * Created: 2/5/2026 9:05:21 AM
5. * Author : Admin
6. */
7. 
   
8. #include <avr/io.h>
9. #include <util/delay.h>
10. #define F_CPU 16000000UL
11. 
    
12. const char MCP23017_W=0x40;
13. const char MCP23017_R=0x41;
14. 
    
15. //IOCON.BANK=0
16. enum BANK0{
17. IODIRA=0,IODIRB,IPOLA,IPOLB,GPINTENA,GPINTENB,DEFVALA,
18. DEFVALB,INTCONA,INTCONB,IOCON1,IOCON2,GPPUA,GPPUB,
19. INTFA,INTFB,INTCAPA,INTCAPB,GPIOA,GPIOB,OLATA,OLATB
20. };
21. 
    
22. 
    
23. void mcp23017_write(char address,char data){
24. twi_start();
25. /*Select the write address*/
26. twi_write(MCP23017_W);
27. /*Select a register address*/
28. twi_write(address);
29. /*Send configuration data*/
30. twi_write(data);
31. twi_stop();
32. }
33. 
    
34. unsigned char mcp23017_read(char address){
35. /*Select a specific address*/
36. twi_start();
37. twi_write(MCP23017_W);
38. twi_write(address);
39. twi_stop();
40. /*Read data from the given address*/
41. twi_start();
42. twi_write(MCP23017_R);
43. unsigned char i2cData=twi_read(1);
44. twi_stop();
45. return i2cData;
46. }
47. 
    
48. const char key_16[4][4]={'1','2','3','A',
49. '4','5','6','B',
50. '7','8','9','C',
51. '*','0','#','D'};
52. 
    
53. char keyScan(void){
54. char data=0,temp,key;
55. for(char i=0;i<4;i++){
56. data=0xFF;
57. data&=~(1<<i);
58. mcp23017_write(OLATA,data);
59. _delay_ms(5);
60. data=mcp23017_read(GPIOA);
61. data&=0xF0;
62. if((data&0x10)==0) {temp=key_16[i][0]; break;}
63. else if((data&0x20)==0){temp=key_16[i][1]; break;}
64. else if((data&0x40)==0){temp=key_16[i][2]; break;}
65. else if((data&0x80)==0){temp=key_16[i][3]; break;}
66. else temp=0;
67. _delay_ms(10);
68. }
69. return temp;
70. }
71. 
    
72. int main(void)
73. {
74. /* Replace with your application code */
75. lcd_init();
76. twi_init();
77. lcd_text("ATMEGA644P TWI");
78. lcd_xy(1,2);
79. lcd_text("MCP23017 KeyPad");
80. _delay_ms(5000);
81. lcd_clear();
82. //Key Pad Init
83. mcp23017_write(IODIRA,0xF0);
84. mcp23017_write(GPPUA,0xF0);
85. char temp,charCount=0,newLine=0,line=1;
86. while (1)
87. {
88. temp=keyScan();
89. if(temp!=0){
90. lcd_data(temp);
91. charCount++;
92. _delay_ms(500);
93. }
94. if(charCount>16){
95. newLine=1;
96. charCount=0;
97. line+=1;
98. }
99. if(newLine){
100. newLine=0;
101. if(line==2) lcd_xy(1,2);
102. else{
103. lcd_xy(1,1);
104. lcd_command(0x01);
105. _delay_ms(5);
106. line=1;
108. }
109. }
110. }
111. }
112. 
     

We need to add the "twi.c" to project before the twi function can be called. 

• "twi.c"

1. /*
2. * twi.c
3. *
4. * Created: 2/4/2026 10:22:02 AM
5. * Author: Admin
6. */
7. 
   
8. #include <avr/io.h>
9. #include <util/delay.h>
10. #define F_CPU 16000000UL
11. 
    
12. 
    
13. void twi_init(void){
14. TWSR|=0x00; //Prescaler Selection Bit
15. TWBR=0x0F; //Baud Rate Generator
16. TWCR=(1<<TWEN); //Enable The TWI Module
17. PORTC|=(1<<0);
18. PORTC|=(1<<1);
19. }
20. 
    
21. void twi_start(void){
22. TWCR=(1<<TWINT)|(1<<TWSTA)|(1<<TWEN);
23. while((TWCR&(1<<TWINT))==0);
24. }
25. 
    
26. void twi_write(unsigned char data){
27. TWDR=data;
28. TWCR=(1<<TWINT)|(1<<TWEN);
29. while((TWCR&(1<<TWINT))==0);
30. }
31. 
    
32. unsigned char twi_read(char ACK){
33. if(ACK==0)
34. TWCR=(1<<TWINT)|(1<<TWEN)|(1<<TWEA);
35. else
36. TWCR=(1<<TWINT)|(1<<TWEN);
37. while((TWCR&(1<<TWINT))==0);
38. return TWDR;
39. }
40. 
    
41. void twi_stop(){
42. TWCR=(1<<TWINT)|(1<<TWEN)|(1<<TWSTO);
43. _delay_us(10);
44. }

 

•  Schematic

 

Proteus Circuit and Simulation

Keypad Scanning

•  ATMega644P AVR Board Experiment

 

 

AVR Prototype Board Experiment

 

AVR Prototype Board Experiment

 

This PCB was offered by PCBWay (pcbway.com).

I have been using PCBWay for many years now. PCBWay fabricate PCBs at low cost, fast processing time for only 24 hours, and fast delivery time using any carrier options. This double side 10cmx10cm can be fabricate at only 5USD for 5 to 10pcs by PCBWay. It's a standard PCB with silk screen and solder mask.

10 PCBs for only 5USD

 

For different size of PCB we can instantly quote on PCBWay website using a zip PCB Gerber file without account.

PCBWay Instant Quote

 

There's on port left GPB. So I added one more keypad port.

Two Keypad Ports

 Source Code:

1. /*
2. * 10-i2c_mcp23017_keypad_2.c
3. *
4. * Created: 2/5/2026 3:14:18 PM
5. * Author : Admin
6. */
7. 
   
8. #include <avr/io.h>
9. #include <util/delay.h>
10. #define F_CPU 16000000UL
11. 
    
12. const char MCP23017_W=0x40;
13. const char MCP23017_R=0x41;
14. 
    
15. //IOCON.BANK=0
16. enum BANK0{
17. IODIRA=0,IODIRB,IPOLA,IPOLB,GPINTENA,GPINTENB,DEFVALA,
18. DEFVALB,INTCONA,INTCONB,IOCON1,IOCON2,GPPUA,GPPUB,
19. INTFA,INTFB,INTCAPA,INTCAPB,GPIOA,GPIOB,OLATA,OLATB
20. };
21. 
    
22. 
    
23. void mcp23017_write(char address,char data){
24. twi_start();
25. /*Select the write address*/
26. twi_write(MCP23017_W);
27. /*Select a register address*/
28. twi_write(address);
29. /*Send configuration data*/
30. twi_write(data);
31. twi_stop();
32. }
33. 
    
34. unsigned char mcp23017_read(char address){
35. /*Select a specific address*/
36. twi_start();
37. twi_write(MCP23017_W);
38. twi_write(address);
39. twi_stop();
40. /*Read data from the given address*/
41. twi_start();
42. twi_write(MCP23017_R);
43. unsigned char i2cData=twi_read(1);
44. twi_stop();
45. return i2cData;
46. }
47. 
    
48. //KeyPad at GPA
49. const char key_1[4][4]={'1','2','3','A',
50. '4','5','6','B',
51. '7','8','9','C',
52. '*','0','#','D'};
53. 
    
54. //KeyPad at GPB
55. const char key_2[4][4]={'E','F','G','H',
56. 'I','J','K','L',
57. 'M','N','O','P',
58. 'Q','R','S','T'};
59. //KeyPad at GPA
60. char keyScan_1(void){
61. char data=0,temp,key;
62. for(char i=0;i<4;i++){
63. data=0xFF;
64. data&=~(1<<i);
65. mcp23017_write(OLATA,data);
66. _delay_ms(5);
67. data=mcp23017_read(GPIOA);
68. data&=0xF0;
69. if((data&0x10)==0) {temp=key_1[i][0]; break;}
70. else if((data&0x20)==0){temp=key_1[i][1]; break;}
71. else if((data&0x40)==0){temp=key_1[i][2]; break;}
72. else if((data&0x80)==0){temp=key_1[i][3]; break;}
73. else temp=0;
74. _delay_ms(10);
75. }
76. return temp;
77. }
78. //KeyPad at GPB
79. char keyScan_2(void){
80. char data=0,temp,key;
81. for(char i=0;i<4;i++){
82. data=0xFF;
83. data&=~(1<<i);
84. mcp23017_write(OLATB,data);
85. _delay_ms(5);
86. data=mcp23017_read(GPIOB);
87. data&=0xF0;
88. if((data&0x10)==0) {temp=key_2[i][0]; break;}
89. else if((data&0x20)==0){temp=key_2[i][1]; break;}
90. else if((data&0x40)==0){temp=key_2[i][2]; break;}
91. else if((data&0x80)==0){temp=key_2[i][3]; break;}
92. else temp=0;
93. _delay_ms(10);
94. }
95. return temp;
96. }
97. 
    
98. int main(void)
99. {
100. /* Replace with your application code */
101. lcd_init();
102. twi_init();
103. lcd_text("ATMEGA644P TWI");
104. lcd_xy(1,2);
105. lcd_text("MCP23017 KeyPad");
106. _delay_ms(5000);
107. lcd_clear();
108. //Key Pad Init
109. mcp23017_write(IODIRA,0xF0);
110. mcp23017_write(GPPUA,0xF0);
111. mcp23017_write(IODIRB,0xF0);
112. mcp23017_write(GPPUB,0xF0);
113. char keyPad_1,keyPad_2,charCount=0,newLine=0,line=1;
114. while (1)
115. {
116. keyPad_1=keyScan_1();
117. if(keyPad_1!=0){
118. lcd_data(keyPad_1);
119. charCount++;
120. _delay_ms(500);
121. }
122. keyPad_2=keyScan_2();
123. if(keyPad_2!=0){
124. lcd_data(keyPad_2);
125. charCount++;
126. _delay_ms(500);
127. }
128. if(charCount>16){
129. newLine=1;
130. charCount=0;
131. line+=1;
132. }
133. if(newLine){
134. newLine=0;
135. if(line==2) lcd_xy(1,2);
136. else{
137. lcd_xy(1,1);
138. lcd_command(0x01);
139. _delay_ms(5);
140. line=1;
142. }
143. }
144. }
145. }

Schematic:

Schematic

 AVR Prototype Board:

AVR Prototype Board

AVR Prototype Board Experiment

 For a full ATMega644P tutorials please visit this page.