Thread: Programming a PIC 16F84 microcontroller in C

First, I must say that I know very few things about programming a microcontroller in C, but I would like to learn.
The following program is not written by me, but I have to write a similiar one (when I press 4 keys from a mini keyboard with 12 keys it activates a cylinder lock who will remain open for a certain amount of time) . In order to do this, I have to understand how this program works (this program is written for a keyboard with 16 keys).
If is somebody among you who knows how to program a microcontroller in C, and has enough patience to explain the program listed(I'm reffering to every line of code ), I would really appreciate it.

Code:

#pragma chip PIC16F84, core 14, code 1024, ram 12 : 0x4F
mapped_into_bank_1

#define INT_min_style
#pragma config_def 0x0111

/* registers from bank 1*/
#pragma char TMR0	@ 0x1
#pragma char PCL0	@ 0x2
#pragma char STATUS0	@ 0x3
#pragma char FSR0	@ 0x4
#pragma char PORTA	@ 0x5
#pragma char PORTB	@ 0x6
#pragma char EEDATA	@ 0x8
#pragma char EEADR	@ 0x9
#pragma char PCLAT0	@ 0x0A

/* registers from bank 2*/
#pragma char OPTION	@ 0x81
#pragma char PCL1	@ 0x82
#pragma char STATUS1	@ 0x83
#pragma char FSR1	@ 0x84
#pragma char TRISA	@ 0x85
#pragma char TRISB	@ 0x86
#pragma char EECON1	@ 0x88
#pragma char EECON2	@ 0x89
#pragma char PCLATH1	@ 0x8A

/*define bits port B*/
#pragma bit RB4		@ 6.4
#pragma bit RB5		@ 6.5
#pragma bit RB6		@ 6.6
#pragma bit RB7		@ 6.7

/*define signals for LED-s, buzz, sensor,cylinder lock and selection*/
#pragma bit	SUPER_LED	@ 5.3
#pragma bit	POWER_LED	@ 5.4
#pragma bit	FULL_LED	@ 6.0
#pragma bit	OPEN_LED	@ 6.1
#pragma bit	SOUND_SIG	@ 5.0
#pragma bit	YALE_SIG	@ 5.1
#pragma bit	SENZOR_SIG	@ 5.2
#pragma bit	SEL0		@ 6.2
#pragma bit	SEL1		@ 6.3

/*functions definitions for turning ON/OFF LED-S*/
#define SUPER_LED_ON	output_low(SUPER_LED)
#define SUPER_LED_OFF	output_high(SUPER_LED)
#define POWER_LED_ON	output_low(POWER_LED)
#define POWER_LED_OFF	output_high(POWER_LED)
#define FULL_LED_ON	output_low(FULL_LED)
#define FULL_LED_OFF	output_high(FULL_LED)
#define OPEN_LED_ON	output_low(OPEN_LED)
#define OPEN_LED_OFF	output_high(OPEN_LED)

/*functions definitions for activation/deactivation signal commands)
#define SOUND_SIG_ON	output_high(SOUND_SIG)
#define SOUND_SIG_OFF	output_low(SOUND_SIG)
#define YALE_SIG_ON	output_high(YALE_SIG)
#define YALE_SIG_OFF	output_low(YALE_SIG)

/*signals selection for activation of a column*/
#define COL1	(output_low(SEL0);output_low(SEL1);)
#define COL2	(output_low(SEL0);output_high(SEL1);)
#define COL3	(output_high(SEL0);output_low(SEL1);)
#define COL4	(output_high(SEL0);output_high(SEL1);)

/*read signals from the keyboard line*/
#define LINE1		(!input(RB7))
#define LINE2		(!input(RB6))
#define LINE3		(!input(RB5))
#define LINE4		(!input(RB4))
#define SENSOR_READ 	(input(SENSOR_SIG))
/*sensor: 1- door open; 0- door close */
/*set direction ports PIC: 1 - enter; 0 - exit*/
#define TRISB_VAL 0b00000000
#define TRISA_VAL 0b00000000

/*structure of the control register for interuptions*/
struct (
	short int RBIF;
	short int INTF;
	short int TOIF;
	short int RBIE;
	short int INTE;
	short int TOIE;
	short int PEIE;
	short int GIE;
) INTCON;
#define byte INTCON	= 0x0B

/*******************************yale.c**********************************/

#include "16F84.h"

#fuses HS,NOWDT, NOPROTECT, PUT
#use DELAY(clock=10000000)
#use fast_io(A)
#use fast_io(B)

int StareInt;
int NrCodes;
void SleepInterrupt()
{
	int code;

	if(!LINE4) StareInt=3;
/*if LINE4 is not active, button # hasn't been pressed and goes into sleep again*/
	else
	{
		INTCON.RBIF=0;
		POWER_LED_ON;
		COL1;
		code=ReadCode();	
		if(cod==-1) StareInt=3;		/*Cancel*/
		else
			StareInt=VerifyCode(code);
	}
	return;
}

int ReadCodeMem(int index)
{
	int adr=index*2, vall,valh;
	valh=read_EEPROM(adr);
	vall=read_EEPROM(adr+1);
	return valh*256+vall;
}

void WriteCodeMem(int index, int val)
{
	int valh, vall, adr;
	adr=index * 2;
	vall=val / 256;
	valh=val % 256;
	write_EEPROM(adr, valh);
	write_EEPROM(adr+1,vall);
}

int VerifyCode(int code)
{
	int i;
	if(ReadCodeMem(0)==code || ReadCodeMem(1)==cod) return 1;   /*supervisor*/

	for(i=2;i<16;i++)
		if(ReadCodeMem(i)==code) return 2;        /*user*/
	return 0;
}

void InitSleep()
{
	POWER_LED_OFF;
	COL1;
	INTCON.RBIF=1;		/*keyboard interrupt active*/
	StareInt=-1;
	Sleep();
}

int ReadKey()
{
	/*it activates the columns one by one and tests  the lines*/
	COL1;
	if(LINE1) return 1;	/*1*/		 
	if(LINE2) return 2;	/*2*/
	if(LINE3) return 3;	/*3*/
	if(LINE4) return 4;	/*SUPER*/
	COL2;
	if(LINE1) return 5;	/*4*/
	if(LINE2) return 6;	/*5*/
	if(LINE3) return 7;	/*6*/
	if(LINE4) return 8;	/*NEW*/
	COL3;
	if(LINE1) return 9;	/*7*/
	if(LINE2) return 10;	/*8*/
	if(LINE3) return 11;	/*9*/
	if(LINE4) return 12;	/*DELETE*/
	COL4;
	if(LINE1) return 13;	/*#*/
	if(LINE2) return 14;	/*0*/
	if(LINE3) return 15;	/*EXIT*/
	if(LINE4) return 16;	/*CANCEL*/
	return 0;
int IsKey()
{
	if(( key >=1 && key <=3) || (key>=5 && key<=7) || (key>=9 && key<=11) || key==14) return 1;
	return 0;
}

void Beep(int time)
{
	SOUND_SIG_ON;
	delay_ms(time);
	SOUND_SIG_OFF;
}

int ReadCode()
{
	int NrCifre=4;
	int key=0;
	int t,time;
	int Result=0;
	
	/*DIV_64: 25.6 uSec per tic, 6.5536 mSec to roll over setup_counters(RTCC_INTERNAL,RTCC_DIV_64); */
	do{
		set_rtcc(0);	/*start counting*/
		key=0;

		time=153*3;
		do
		{
			key=ReadKey();

			t=get_rtcc();
			if(t==0) time--;
		}while (key && time)
		/*reads until a key is pressed or time expires*/
		if(key!=0)
		{
			if (IsKey(key))
			{
				Result=Result*10+key;
			}
			else if(key==16) return -1; /*Cancel*/
			else
			{
				Beep(100);
				NrCifre++;
			}
			NrCifre--;
		}
		else return -1;
	}while (NrCifre);
	return Result;
}

void OpenDoor()
{
	int t, time;
	YALE_SIG_ON; /*door open*/
	OPEN_LED_ON; /*LED ON - the door is open*/
	Beep(300);   /*sound signal*/

	set_rtcc(0); /*start counting*/
	key=0;

	time=153*10; /*door remains unlock for 10 seconds*/
	do
	{
		t=get_rtcc();
		if( t==0 ) time--;
	}while (SENSOR_READ && time)
	/*reads until a person open the door or time expires*/

	if(time)  /*a person opened the door*/
	{
		time=153*300;	/*after 30 seconds - beeps*/
		do
		{
			t=get_rtcc();
			if(t==0) time--;
		}while(SENSOR_READ && time);
	/*reads until a person close the door or time expires*/

	if(!time)	/*time expires*/
	{
		while(!SENSOR_READ)
		{
					Beep(100);
				/*beeps until door is closed*/
		}/*door closed*/
	}/*door must be closed*/
		YALE_SIG_OFF;
		OPEN_LED_OFF;
		Beep(200);
}

void Edit();
{
	int t, key, counter, state;

	SUPER_LED_ON;
	do
	{
		set_rtcc(0);
		counter=153*10;	/*waiting time 10 seconds*/
		if(NrCodes==30) FULL_LED_ON;
			else	FULL_LED_OFF;
		do
		{
			key=ReadKey();
			t=get_rtcc();
			if(t==0) counter--;
		}while(!key && counter);
		/*until a key is pressed or time expires*/
	if (counter)
	{
	  if(key)
	  {
	     switch(key)
	     {
	     case 8 :		/*NEW*/
			if(NrCodes=30) Beep(200); 
			else
			{
				key=ReadCode(); /*reads a code*/
				if(key != -1)
					state=VerifyCode(key);
					if(state!=0) Beep(200);
					   else
					   {
						counter=153*3;
						set_rtcc();
						do
						{
							state=ReadKey();
							t=get_rtcc(0);
							if(t==0) counter--;
						}while(!state && counter);
						if(state!=4 !counter)
						{
						    NrCodes++;
						    for (t=2; t<=31 && ReadCodeMem(t) !=0; t++)
						    if(t!=32) WriteCodeMem(t,key);
						}
						else if(state==4)
						{
						    if(ReadCodeMem(0)==-1)
							WriteCodeMem(0,key);
						    else if(ReadCodeMem(1)==-1)
							WriteCodeMem(1,key);
						}
						Beep(300);
					    }
			}
			break; /*NEW*/
	   case 12:	/*Del*/
		if (NrCodes>0)
			key=ReadKey();	/*read code*/
		if (key!=-1)
			state=VerifyCode();
		if (state==0) Beep(200);	/*code dosn't exist*/
		else
		{
			if(state==2)	/*a user is deleted*/
			{
				for(t=2; t<=31 && ReadCodeMem(t) != key; t++);
				WriteCodeMem(t,0); /*user t deleted*/
				NrCodes--;
			}
			else
			{
			  if(ReadCodeMem(0)==key && ReadCodeMem(1)!=-1)
				WriteCodeMem(0,0);
			  else if(ReadCodeMem(1)==key && ReadCodeMem(0)!=-1)
				WriteCodeMem(1,0);
			}
		}
		Beep(300);
		break;
	   case 16: Beep(100); break;  /*Cancel*/
	    }
	}
       }
      }while(key!=15 && counter); /*Exit*/
      Beep(300);
      SUPER_LED_OFF;
      FULL_LED_OFF;
}

void main
{
	int time,t,key;

	set_trisa(TRISA_VAL);
	set_trisb(TRISB_VAL);

	WriteCodeMem(0,1234);	/*initial code for first suprvisor*/
	for(t=1; t<=31; t++)
	   WriteCodeMem(t,0);	
	NrCodes=0;
	InitSleep();
	StateInt=-1;
	while(1)
	{
		switch (StateInt)
		{
			case 3 : Beep(300);	/*Cancel*/
			case 2 : OpenDoor(); break;	/*user*/
			case 1 : set_rtcc(0);	/*supervisor*/
				 time=153*3;
				 do
				 {
				  key=ReadKey();
				  t=get_rtcc();
				  if(t==0) time--;
				 }while(key && time);
				/*read untile a key is pressed or time expires*/
				 if (time && key==4) /*SUPER is pressed*/
				 	OpenDoor();
				 else if(!time)		/*goes into EDIT mode*/
					Edit();
				 else Beep(200);
				 break;
		}
		InitSleep();
	}
}