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.

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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: