ECE 447 Lecture 1012 Keypads ECE 447 Matrix

ECE 447: Lecture 1012 Keypads

ECE 447: Matrix Keypad

ECE 447: Matrix Keypad Microcontroller Interface

ECE 447: Matrix Keypad - Scanning 1 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 1 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 0 1 1 1

Matrix Keypad ECE 447: Matrix- Scanning Keypad - Scanning 1 0 1 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 1 1 0 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 1 1 1 0

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning PC 0 PC 1 PC 2 PC 3 PC 4 PC 5 PC 6

ECE 447: Matrix Key Codes outputs 11110000 F 0 inputs

ECE 447: Key Scanning Function while (1) { do ( PORTC = "XXXX 0000" while ( PORTC = "X 111 XXXX"); } Wait until any key pressed c=decode_key(); . . . do something dependent on the key being pressed. . . Decode the key being pressed PORTC = "XXXX 0000" while (PORTC != "X 111 XXXX") /* do nothing */ Wait until all keys released

ECE 447: Key Scanning Function int decode_key() { PORTC = "XXXX 1110" if ( PORTC != "X 111 XXXX”) return decode_output (PORTC, 1) else { PORTC = "XXXX 1101" if ( PORTC != "X 111 XXXX") return decode_output(PORTC, 2) } else { PORTC = "XXXX 1011" if ( PORTC != "X 111 XXXX") return decode_output (PORTC, 3) } else { PORTC = "XXXX 0111" if ( PORTC != "X 111 XXXX") return decode_output (PORTC, 4) else return NONE_KEY_PRESSED; } check Row 1 check Row 2 check Row 3 check Row 4

Possible Key Decoding Procedure (3) ECE 447: Key Scanning Function Decoding a column XCCCXXXX • Three bits of interest • Three combinations valid (“ 110”, “ 101”, “ 011”) • Decoding column possible

ECE 447: Matrix Key Codes 11110000 F 0 inputs

ECE 447: Matrix Key Codes 11110000 outputs F 0

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 0 0 outputs 0 0 1 inputs 1 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 0 0 outputs 0 0 1 inputs 1 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 0 0 outputs 0 0 1 inputs 1 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 0 0 outputs 0 0 1 inputs 0 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 1 1 outputs 1 0 1 inputs 0 1

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 1 1 outputs 1 0 1 inputs 0 1

ECE 447: Keypad Matrix - Scanning 1 1 outputs 0 1 1 inputs 1 0

Keypad - Scanning ECEMatrix 447: Matrix Keypad - Scanning 1 1 outputs 0 1 1 inputs 1 0

Simplified Procedure (4) – ECE 447: Key. Decoding Scanning Function Alternative decode_key() { unsigned char keys = [NONE, TWO, …, TWELVE]; for (i=0, i<=12, i++) { PORTC = keys[i] if (PORTC == keys[i] return i; } return UNKNOWN; }

ECE 447: Matrix Key Codes ONE TWO THREE FOUR FIVE SIX SEVEN EIGHT NINE TEN ELEVEN TWELVE NONE 11110000 F 0

ECE 447: Key Scanning Function – No Debounce while (1) { do ( PORTC = "XXXX 0000" while ( PORTC = "X 111 XXXX"); } Wait until any key pressed c=decode_key(); . . . do something dependent on the key being pressed. . . Decode the key being pressed PORTC = "XXXX 0000" while (PORTC != "X 111 XXXX") /* do nothing */ Wait until all keys released

Key Bouncing ECE 447: Key Bounce key bounce, t. BOUNCE typically, t. BOUNCE < 10 ms

Keypad Bouncing ECE 447: Key Bounce key bounce, t. BOUNCE typically, t. BOUNCE < 10 ms NONE

Keypad in Software ECE 447: Debouncing Key Bounce key bounce, t. BOUNCE typically, t. BOUNCE < 10 ms wait debouncing period wait until any key pressed NONE decode_key; action dependent on the key wait until all keys released NONE wait debouncing period wait until any key pressed

ECE 447: Key Scanning Function – Key Decoding Procedure (7) with Debounce while (1) { while (key_decode() == NONE) /* do nothing */ ; wait debouncing period(); c=decode_key(); . . . do something dependent on the key being pressed. . . while(key_decode()!=NONE) /* do nothing */ ; wait debouncing period(); } Wait until any key pressed Decode the key being pressed Wait until all keys released

2 out 2 ofof 7 Keypad ECE 447: 7 Keypad C

ECE 447: 2 of 7 Keypad Microcontroller Interface

ECE 447: 2 of 7 Keypad Scanning 0 C

2 out of 2 7 Keypad - Scanning ECE 447: of 7 Keypad Scanning 1 1 1 0 1 0 C

ECE 447: 2 of 7 Keypad Scanning Function decode_key() { unsigned char keys = [NONE, TWO, …, TWELVE]; for (i=0, i<=12, i++) { PORTC = keys[i] if (PORTC == keys[i] return i; } return UNKNOWN; }

ECE 447: 2 of 7 Key Codes ONE TWO THREE FOUR FIVE SIX SEVEN EIGHT NINE TEN ELEVEN TWELVE NONE

ECE 447: 2 of 7 Keypad Microcontroller Interface

ECE 447: 2 of 7 Keypad Scanning Function (Simplified) decode_key() { unsigned char keys = [NONE, TWO, …, TWELVE]; code = PORTC for (i=0, i<=12, i++) { if (code == keys[i] return i; } return UNKNOWN; }

ECE 447: 2 of 7 Keypad Scanning Function while (1) { while (decode_key() == NONE) /* do nothing */ ; wait debouncing period(); c=decode_key(); . . . do something dependent on the key being pressed. . . while(decode_key()!=NONE) /* do nothing */ ; wait debouncing period(); } Wait until any key pressed Decode the key being pressed Wait until all keys released

ECE 447: 2 of 7 Keypad Hardware Key Debouncing Debounce in Hardware

ECE 447: 2 of 7 Keypad Hardware Key Debouncing Debounce in Hardware Capacitors associated with all pull-up resistors