File content as of revision 0:b44cdf7cb6a5:

#include "mbed.h"
#include <map>

//Initialize serial comms
Serial pc(USBTX, USBRX);

PwmOut PWM1(p21);

DigitalOut row1(p25);
DigitalOut row2(p22);
DigitalOut row3(p23);
DigitalOut row4(p24);

DigitalIn col1(p20);
DigitalIn col2(p19);
DigitalIn col3(p18);
DigitalIn col4(p17);
Timer t1;

//map
map<int, char> keypadMap;

//Mores Code -> Character Map
void init(){
        keypadMap[0x11]='1';
        keypadMap[0x12]='2';
        keypadMap[0x14]='3';
        keypadMap[0x18]='A';
        keypadMap[0x21]='4';
        keypadMap[0x22]='5';
        keypadMap[0x24]='6';
        keypadMap[0x28]='B';
        keypadMap[0x41]='7';
        keypadMap[0x42]='8';
        keypadMap[0x44]='9';
        keypadMap[0x48]='C';
        keypadMap[0x81]='*';
        keypadMap[0x82]='0';
        keypadMap[0x84]='#';
        keypadMap[0x88]='D';
}

int main() {
    init();
    //Initialize rows to 0
    row1 = 0;
    row2 = 0;
    row3 = 0;
    row4 = 0;
    t1.start();
    int input = 0x00;
    while(1) {
       //Keep each led lit for 4ms
       switch(t1.read_ms()%4){
                        case 0:
                        row1 = 1;
                        input |= 0x10;
                        row4 = 0;
                        break;
                        case 1:
                        row2 = 1;
                        input |= 0x20;
                        row1 = 0;
                        break;
                        case 2:
                        row3 = 1;
                        input |= 0x40;
                        row2 = 0;
                        break;
                        case 3:
                        row4 = 1; 
                        input |= 0x80;
                        row3 = 0;
                        break; 
                        }
     if(col1 == 1)
     input |= 0x01;
     else if(col2 == 1)
     input |= 0x02;
     else if(col3 == 1)
     input |= 0x04;
     else if(col4 == 1)
     input |= 0x08;
     
     char c = keypadMap[input]; //assign charcter based on input
     
     if(c != 0){
     pc.printf("%c\r",c);  //print input and char
     }
    
     
     input = 0x00;
     
       
    }
}