Getting an input from a user may seem trivial, but in real word it will lead to resolve some problems like switch bounce, input correction, input validation, polling function in each major loop of the program, and so on... Here is a very convenient way to solve them : this interrupt-based keypad library will do it for you.

Page index :

• Why another PIC Keypad LIBRARY ?
• Library functions
• Configuration
• Circuit example
• MikroC source code example
• Project download

Why another PIC Keypad LIBRARY ?

There are already tons of keypad PIC libraries on the web, but I think this one will be the most universal and versatile, featuring :

• keypad up to 8x8 or buttons up to 8
• fully configurable I/O :
  • user defined ports
  • in keypad mode row port and column port may be different
  • user defined bits in port
  • user defined rows and columns number
• user defined character lookup table
• user defined erase and enter keys
• works on interrupt : no polling necesary, no key lost
• auto debounce, delay is user defined
• switchable typematic (auto-repeat) mode at run time, rate is user defined
• switchable linear/circular buffer mode at run time
• input is available at any time in a string buffer
• maximum input size is user defined
• other functions :
  • last key entered
  • keypad status...

Learn more below :

Library Functions

PROTOTYPE	void    kp_init()
PARAMETERS	none
RETURNS	nothing
DESCRIPTION	prepare the PIC keypad and button library. this function must be called before enabling timer interrupt.
REQUIRES	the file keypad_cfg.h must be set accordingly to user's hardware (see below)
EXAMPLE	kp_init() ;

PROTOTYPE	void    kp_isr()
PARAMETERS	none
RETURNS	nothing
DESCRIPTION	this function must not be called directly by user, but must be placed in the timer interrupt() function. the input is stored in buffer kp_buf, defined as a pointer to char.
REQUIRES	kp_init() must have been called
EXAMPLE	void    interrupt(void)         {         if(INTCON.T0IF)                         // timer 0 overflow ?                 {                 kp_isr() ;                      // call keypad service routine                 INTCON.T0IF = 0 ;               // done                 }         }

Configuration

Keypad configuration is defined in file keypad_cfg.h, you can change it depending on your hardware and preferences :

SYMBOL	USAGE	EXAMPLE
KEYPAD_MODE	define this symbol if you are using a keypad (rows and colums) do not define this symbol if you are using buttons (colums only)	#define KEYPAD_MODE
KP_ROW_PORT	PORT where rows are connected to (only if KEYPAD_MODE is defined)	#define KP_ROW_PORT     PORTB
KP_ROW_TRIS	TRIS direction register corresponding to KP_ROW_PORT (only if KEYPAD_MODE is defined)	#define KP_ROW_TRIS     TRISB
KP_ROW_BITNUM	bit number of the first row in the PORT, other bits must be next and contiguous (only if KEYPAD_MODE is defined)	#define KP_ROW_BITNUM   0
KP_ROW_NUMBER	number of rows (only if KEYPAD_MODE is defined)	#define KP_ROW_NUMBER   3
KP_COL_PORT	PORT where columns are connected to. Each column input must be pulled down with a 10 K resistor.	#define KP_COL_PORT     PORTB
KP_COL_TRIS	TRIS direction register corresponding to KP_COL_PORT	#define KP_COL_TRIS     TRISB
KP_COL_BITNUM	bit number of the first row in the PORT, other bits must be next and contiguous	#define KP_COL_BITNUM   3
KP_COL_NUMBER	number of columns	#define KP_COL_NUMBER   4
KP_SCAN_CODES	scan codes lookup table keypad must be considered this way : the top left key is the first one, the bottom right key is the last one. you have to read from top to bottom and from left to right : * 7 4 1 0 8 5 2 # 9 6 3	#define KP_SCAN_CODES   "*7410852#963"
KP_ERASE	erase key, must be one in KP_SCAN_CODES string don't define it if you don't need an erase key	#define KP_ERASE        '*'
KP_ENTER	enter key, must be one in KP_SCAN_CODES string don't define it if you don't need an enter key	#define KP_ENTER        '#'
KP_MAX_LENGTH	maximum input length	#define KP_MAX_LENGTH   16
KP_TMR_REPEAT	typematic rate, must be set depending on timer overflow period and user's preferences. you can use this formula : KP_TMR_REPEAT = (Fosc / 4 / TMR_PRESCALER / (2 ^ TMR_BITS)) * DELAY_REPEAT where : Fosc is the frequency of the oscillator in Herz. For example if you are using a 8 Mhz crystal with HS clock mode, then Fosc = 8000000 TMR_PRESCALER is the prescaler (or postscaler if any) value of your timer. For example if you are using a 1:1 prescaler then TMR_PRESCALER = 1 TMR_BITS is the number of bits of your timer, it is either 8 or 16 DELAY_REPEAT is the delay in second before the next auto repeat. when using a PIC16F877A @ 8 Mhz with 8 bit TMR0 and no prescaler, if you want an auto repeat rate of 300 ms, use : KP_TMR_REPEAT = (8000000 / 4 / 1 / (2 ^ 8)) * .3 = 2343	#define KP_TMR_REPEAT   2343
KP_TMR_DEBOUNCE	debounce time, must be set depending on timer overflow period and user's preferences. you can use this formula : KP_TMR_DEBOUNCE = (Fosc / 4 / TMR_PRESCALER / (2 ^ TMR_BITS)) * DEBOUNCE_DELAY where : Fosc is the frequency of the oscillator in Herz. For example if you are using a 8 Mhz crystal with HS clock mode, then Fosc = 8000000 TMR_PRESCALER is the prescaler (or postscaler if any) value of your timer. For example if you are using a 1:1 prescaler then TMR_PRESCALER = 1 TMR_BITS is the number of bits of your timer, it is either 8 or 16 DEBOUNCE_DELAY is the delay in second before the keyboard to be read again. when using a PIC16F877A @ 8 Mhz with 8 bit TMR0 and no prescaler, if you want a debounce time of 30 ms, use : KP_TMR_DEBOUNCE  = (8000000 / 4 / 1 / (2 ^ 8)) * .03 = 234	#define KP_TMR_DEBOUNCE   234
KP_MAX_LENGTH	maximum input length	#define KP_MAX_LENGTH   16

Click on the picture to enlarge

Columns must be pulled down, use resistors from 4K7 to 22K. Don't forget that columns are from bottom to top, and rows for left to right. This arrangement is due to code simplification, because library can work with buttons too. If you use buttons only instead of keypad, they must also be pulled down. In this case, there is no row but only columns.

MIKROC SOURCE CODE EXAMPLE

Here is the mikroC source code of the program example. You have to use the zipped mikroC project to build it.

/* ******************************************************************************* * PIC ADVANCED UNIVERSAL KEYPAD LIBRARY ******************************************************************************* * * source code example for mikro C compiler * feel free to use this code at your own risks * * target : PIC16F877A, 8 Mhz crystal * HS clock, no watchdog. * * Author : Bruno Gavand, October 2007 * see more details on http://www.micro-examples.com/ * * This program shows how to use the library : * 4 bit LCD is connected to PORTD (EasyPIC4 board) * edit keypad_cfg.h header file to configure your own keypad * * LCD Line 1 : welcome message and keypad status symbols * LCD Line 2 : string as keyed in by user * * type 123 + enter to toggle circular/linear buffer mode * type 321 + enter to toggle typematic mode on/off * ******************************************************************************* */ #include "keypad_lib.h" // keypad library header, includes also user's settings /* * LCD custom characters */ const char erase_char[] = {2,6,14,31,14,6,2,0} ; // erase key typed const char enter_char[] = {1,1,5,13,31,12,4,0} ; // enter key typed const char full_char[] = {0,10,21,10,21,10,0,0} ; // buffer is full const char hit_char[] = {0,4,4,4,31,14,4,0} ; // a key is pressed const char circ_char[] = {16,24,28,25,19,7,3,1} ; // buffer is in circular mode const char type_char[] = {31,21,21,4,4,4,4,14} ; // typematic enabled /* * print custom character pointed to by def at line pos_row column pos_char on LCD */ void CustomChar(const char *def, unsigned char n, char pos_row, char pos_char) { char i ; LCD_Cmd(64 + n * 8) ; for(i = 0 ; i <= 7 ; i++) { LCD_Chr_Cp(def[i]) ; } LCD_Cmd(LCD_RETURN_HOME) ; LCD_Chr(pos_row, pos_char, n) ; } /* * interrupt routine, called on each timer0 overflow */ void interrupt(void) { if(INTCON.T0IF) // timer 0 overflow ? { kp_isr() ; // call keypad service routine INTCON.T0IF = 0 ; // done } } /* * program entry */ void main() { /* * init LCD */ LCD_Init(&PORTD) ; LCD_Cmd(LCD_CLEAR) ; LCD_Out(1, 1, "KeypadLib") ; LCD_Cmd(LCD_SECOND_ROW) ; /* * init keypad and library */ kp_init() ; /* * configure timer0 rollover interrupt * period is Fosc / 4 / 256 */ OPTION_REG = 0x80 ; // start timer 0, no prescaler INTCON = 0xA0 ; // allow timer 0 interrupt for(;;) // forever { if(kp_hit()) // if a key is pressed { LCD_Cmd(LCD_CURSOR_OFF) ; // no cursor CustomChar(hit_char, 1, 1, 12) ; // display hit symbol if(kp_enter()) // if enter key is pressed { CustomChar(enter_char, 2, 1, 13) ; if(strcmp(kp_buf, "123") == 0) // if entry is 123 { if(kp_circular()) // toggle buffer circular/linear mode { kp_setLinear() ; } else { kp_setCircular() ; } } else if(strcmp(kp_buf, "321") == 0) // if entry is 321 { if(kp_typematic()) // toggle typematic (auto-repeat) mode { kp_unsetTypematic() ; } else { kp_setTypematic() ; } } kp_flush() ; // clear entry buffer } else { LCD_Chr(1, 13, ' ') ; } /* * buffer full symbol */ if(kp_full()) { CustomChar(full_char, 0, 1, 11) ; } else { LCD_Chr(1, 11, ' ') ; } /* * erase key symbol */ if(kp_erase()) { CustomChar(erase_char, 3, 1, 14) ; } else { LCD_Chr(1, 14, ' ') ; } /* * circular mode symbol */ if(kp_circular()) { CustomChar(circ_char, 4, 1, 15) ; } else { LCD_Chr(1, 15, ' ') ; } /* * typematic mode symbol */ if(kp_typematic()) { CustomChar(type_char, 5, 1, 10) ; } else { LCD_Chr(1, 10, ' ') ; } LCD_Chr(1, 16, kp_last()) ; // display last char keyed in LCD_Chr(1, 12, ' ') ; // clear hit symbol LCD_Out(2, 1, " ") ; // clear old buffer display LCD_Out(2, 1, kp_buf) ; // display current buffer LCD_Cmd(LCD_BLINK_CURSOR_ON) ; // blink cursor } } }

PROJECT DOWNLOAD

You can use this software as you wish, if you accept to do it at your own risks.

Download PIC Keypad Library C source code with demo example for mikroC : zipped file, 6 Ko 

content of the archive :

• keypad_lib.c, 10 Ko : library C source code
• keypad_lib.h, 3 Ko : library C definitions
• keypad_cfg.h, 2 Ko : user's configuration
• keypad.ppc, 1 Ko : mikroC project file
• keypad.c, 8 Ko : demo example for PIC16F877A

You can get mikroC from here : http://www.mikroe.com/en/compilers/mikroc/pic/

Please report any bug, comment or suggestion in my forums. Thanks !