How to interface RFID with PIC18F4550 Microcontroller

[barish]

// Program to interface RFID module using EUSART in PIC18F4550



// Configuration bits

/* _CPUDIV_OSC1_PLL2_1L,  // Divide clock by 2

_FOSC_HS_1H,           // Select High Speed (HS) oscillator

_WDT_OFF_2H,           // Watchdog Timer off

MCLRE_ON_3H            // Master Clear on

*/



#define FREQ 12000000

#define baud 9600

#define spbrg_value (((FREQ/64)/baud)-1)

#define rs LATA.F0

#define rw LATA.F1

#define en LATA.F2

#define lcdport LATB



unsigned char rx_data();

void lcd_ini();

void lcdcmd(unsigned char);

void lcddata(unsigned char);

unsigned char data[]="Unique ID No.";

unsigned char card_id[12];

unsigned int i=0,pos;



void main()

{

TRISB=0;			// Set Port B as output port

LATB=0;

TRISA=0;

LATA=0;

SPBRG=spbrg_value;		// Fill SPBRG register to set the baud rate

RCSTA.SPEN=1;			// To activate serial port (Tx and Rx pins)

RCSTA.CREN=1;			// To enable continuous reception

PIE1.RCIE=1;			// To enable the Reception (Rx) Interrupt

INTCON.GIE=1;

INTCON.PEIE=1;

lcd_ini();			// LCD initialization

while(data!='')

{

lcddata(data);	// To send characters one by one from 'data' array

i++;

}

while(1)

{

i=0;

while(i<12);

lcdcmd(0xC0);

i=0;

while(i<12)

{

lcddata(card_id);	// Print the 12 byte received data

i++;

}

}

}





void interrupt()

{

card_id=RCREG;		// Store the received data byte by byte

i++;

}



void lcd_ini()

{

lcdcmd(0x38);		// Configure the LCD in 8-bit mode, 2 line and 5x7 font

lcdcmd(0x0C);		// Display On and Cursor Off

lcdcmd(0x01);		// Clear display screen

lcdcmd(0x06);		// Increment cursor

lcdcmd(0x80);		// Set cursor position to 1st line, 1st column

}



void lcdcmd(unsigned char cmdout)

{

lcdport=cmdout;		//Send command to lcdport=PORTB

rs=0;

rw=0;

en=1;

Delay_ms(10);

en=0;

}



void lcddata(unsigned char dataout)

{

lcdport=dataout;	//Send data to lcdport=PORTB

rs=1;

rw=0;

en=1;

Delay_ms(10);

en=0;

}

 

 

In this code how "void interrupt()" function will get executed.  

 

[GANEEV SINGH]

Hi there

PICs can handle atmost one interrupt (if priority is not set) at a time. Thus writing interrupt in front of any function makes it an ISR (interrupt service routine). As in this case, PIE1.RCIE=1; statement is written to enable the USART Rx interrupt; so any interrupt request by Rx's flag will make PIC start executing the void interrupt();

Also this same interrupt function can be used to see if any other interrupt request has been made or not. Refer its datasheet for the same.

Hope this clears your doubt

[barish]

Can we require a assembly function to redirect from 0x0008 or 0x0018 isr location to our c function?

Or simply given code will work?

[GANEEV SINGH]

When writing code in C, PIC only calls one ISR function for all of its interrupts i.e. function with name interrupt(); (here). It is then on the coders side to write such a code that could decide which interrupt to focus on and execute its function(s).

I do not think we can change ISR's address as it is predefined inside the chip. 

[barish]

thank you

if 2 or more interrupts are neede to define then how to regognize them i.e. which interrupt is currently active or triggered.

 

[GANEEV SINGH]

You will need to check their respective flag bits and then accordingly perform any action.

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