Scanning of Keypad (4x4) using timer

Code C - [expand]
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int8 column = 0;
int8 keyindex;
 
void main(void) {
    PAADIR = 0x0F;              //  Set the low its in output.
    ConfigTimer(20);            //  Configure the timer (ex. 20 ms).
    SleepAndWaitInterrupts();   //  That's it, the main program is over.
}
 
 
void TimerISR() {
    column++;                   //  Next column
    if(column == 4) column = 0; //  Back to 0 if more than 3
    PAOUT = 1 << column;
}
 
void PortAISR {
    uint8 line = PAIN;          //  Get thevalue of theinterrupt into line
    // Now you can calculate a unique number between 0 and 15
    // which can be used to identify which key has been pressed.
    switch(line) {
    case 1:
        keyindex = column   
    case 2:
        keyindex = column + 4;
    case 4:
        keyindex = column + 8;
    case 8:
        keyindex = column + 12
    }
    ProcessKey();
}
 
void ProcessKey() {
    //  Do whatever you want with your key index.
}