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

 

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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