ATMega644P TWI PCF8574AP Matrix Keypad LCD

A matrix keypad could save the number of micro-controller I/O usage. For instant a 4x4 matrix keypad uses only 8 pins of a micro-controller but it yield 16 different key values. Using an 8-bit micro-controller digital I/O port is common for most of programmers. 

However when the there is a I/O constraint we need an I/O expansion, for example adding serial interface I/O expansion chip to a micro-controller.These chips need only a few wires of a micro-controller.

16 Key Membrane Switch Keypad 4X4 3X4 Matrix Keyboard For Arduino Diy Kit

 

In this post I will show an example of using the PCF8574AP to make a 4x4 matrix keypad with a character LCD. For more information about using the PCF8574 series please visit these posts,

1. ATMega644P TWI PCF8574 I/O Expansion Interfacing 
2. PIC16F887 PCF8574AP I2C LCD Example using XC8 
3. PIC16F887 PCF8574AP I2C 4x4 KeyPad using XC8 
4. PIC16F887 PCF8574 I2C Example using XC8 
5. A DIY TWI LCD Using PCF8574AP For Arduino 
6. ATMega32 TWI interfaces to PCF8574A parallel port expansion 
7. Reading The Digital Input Output From PCF8574 Using PIC12F629 

The TWI master micro-controller of the ATMega644P periodically scan for any key press. The result of will display on an on-board 16x2 character LCD.

Source Code:

1. /*
2. * 10-i2c_pcf8574ap_keypad.c
3. *
4. * Created: 2/2/2026 9:32:41 PM
5. * Author : Admin
6. */
7. 
   
8. #include <avr/io.h>
9. #include <util/delay.h>
10. #define F_CPU 16000000UL
11. 
    
12. //DIY PCF8574AP LCD Module (A2:A0=0)
13. const char pcf8574_w=0x40;
14. const char pcf8574_r=0x41;
15. //PCF8574 (A2:A0=0)
16. const char pcf8574a_w=0x70;
17. const char pcf8574a_r=0x71;
18. //DIY Arduino PCF8574T LCD Module
19. const char pcf8574T_LCD_W=0x4E;
20. const char pcf8574T_LCD_R=0x4F;
21. 
    
22. void i2cInit(void){
23. TWSR|=0x00; //Prescaler Selection Bit
24. TWBR=0xF0; //Baud Rate Generator
25. TWCR=(1<<TWEN); //Enable The TWI Module
26. PORTC|=(1<<0);
27. PORTC|=(1<<1);
28. }
29. 
    
30. void i2cStart(void){
31. TWCR=(1<<TWINT)|(1<<TWSTA)|(1<<TWEN);
32. while((TWCR&(1<<TWINT))==0);
33. }
34. 
    
35. void i2cWrite(unsigned char data){
36. TWDR=data;
37. TWCR=(1<<TWINT)|(1<<TWEN);
38. while((TWCR&(1<<TWINT))==0);
39. }
40. 
    
41. unsigned char i2cRead(char ACK){
42. if(ACK==0)
43. TWCR=(1<<TWINT)|(1<<TWEN)|(1<<TWEA);
44. else
45. TWCR=(1<<TWINT)|(1<<TWEN);
46. while((TWCR&(1<<TWINT))==0);
47. return TWDR;
48. }
49. 
    
50. void i2cStop(){
51. TWCR=(1<<TWINT)|(1<<TWEN)|(1<<TWSTO);
52. _delay_us(10);
53. }
54. 
    
55. void pcf8574Write(char data){
56. i2cStart();
57. i2cWrite(pcf8574a_w);
58. i2cWrite(data);
59. i2cStop();
60. }
61. 
    
62. char pcf8574Read(void){
63. i2cStart();
64. i2cWrite(pcf8574a_r);
65. char temp=i2cRead(1);
66. i2cStop();
67. return temp;
68. }
69. 
    
70. uint8_t key_16[][4]={'1','2','3','A',
71. '4','5','6','B',
72. '7','8','9','C',
73. '*','0','#','D'};
74. 
    
75. uint8_t keyScan(void){
76. char data=0,temp,key;
77. for(uint8_t i=0;i<4;i++){
78. data=0xFF;
79. data&=~(1<<i);
80. pcf8574Write(data);
81. _delay_ms(5);
82. data=pcf8574Read();
83. data&=0xF0;
84. if((data&0x10)==0) {temp=key_16[i][0]; break;}
85. else if((data&0x20)==0){temp=key_16[i][1]; break;}
86. else if((data&0x40)==0){temp=key_16[i][2]; break;}
87. else if((data&0x80)==0){temp=key_16[i][3]; break;}
88. else temp=0;
89. _delay_ms(10);
90. }
91. return temp;
92. }
93. 
    
94. int main(void)
95. {
96. /* Replace with your application code */
97. i2cInit();
98. lcd_init();
99. lcd_text("ATMega644P TWI");
100. lcd_xy(1,2);
101. lcd_text("PCF8574AP KeyPad");
102. _delay_ms(10000);
103. lcd_clear();
105. char temp,charCount=0,newLine=0,line=1;
106. while (1)
107. {
108. temp=keyScan();
109. if(temp!=0){
110. lcd_data(temp);
111. charCount++;
112. _delay_ms(500);
113. }
114. if(charCount>16){
115. newLine=1;
116. charCount=0;
117. line+=1;
118. }
119. if(newLine){
120. newLine=0;
121. if(line==2) lcd_xy(1,2);
122. else{
123. lcd_xy(1,1);
124. lcd_command(0x01);
125. _delay_ms(5);
126. line=1;
128. }
129. }
130. }
131. }
132. 
     
133. 
     

Schematic:

Schematic and Simulation

Simulation Program

 

ATMega644P Experiment Board:

This PCB was offered by PCBWay.

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