Thread: Random number generator using pic18f4520 in mplab c18 compiler

j is not declared.
i is not volatile

Try setting a flag in your interrupt routine and calling rand from your main()

Oh and you need to

Code:

	
	// Enable all low priority interrupts
	INTCONbits.GIEL = 1;

Have a look at the forums at Microchip and see if you can get a blinking light example and work from that example

Also, where are your config bits?

I think that you should go through a tutorial about how to program the PIC with c language -> A really good site is Gooligum Electronics

hi, what do you mean by 'i is not volatile'? is it i have to set 'i=0' in my main? sorry i'm new in programming.

Sorry I'm new in programming

There is nothing wrong with that.

"Additionally, any global variable which may be modified by the ISR must be declared as 'volatie', to warn the compiler from eleminating apparently redundant references to those variable in the main program" (Meiklehohn D., 2012, 'Lesson 3: inroduction to Interrupts', 'Introduction to PIC Programming: Programming Mid-Range PICs in C' http://www.gooligum.com.au/tutorials...IC_Mid_C_3.pdf)

Go to the Gooligum tutorials - They are good. The section that you want to learn is 'Programming Mid-Range PICs in C'.

hi, i'm working on this project which require two 7-segment to display random numbers between 0-7. These 7-segments is control by a touch sensor. I've revise my code but it's only display 0,7,4,5 and repeat. It's not what i wanted. This is the code:

Code:

#include<p18f4520.h>
#include <stdlib.h>	
#define first 	PORTAbits.RA0
#define middle 	PORTAbits.RA1
#define last	PORTAbits.RA2
#define first1 	PORTAbits.RA3
#define middle1 PORTAbits.RA4
#define last1	PORTAbits.RA5
#define control PORTCbits.RC0


void ISR (void);


char i,start,j,end;


#pragma code L_vector=0x18
void L_vector(void){
_asm goto ISR _endasm
}




#pragma code
#pragma interruptlow ISR


void ISR(void)


{
if(INTCONbits.TMR0IF)
{


TMR0H=0xC2;
TMR0L=0xF7;
i=rand();
start=(i+TMR0H)%8;
j=rand();
end=(j+TMR0L)%8;
INTCONbits.TMR0IF=0;
}
}


void main(void){




i=0; 
INTCONbits.GIEH=0;
INTCONbits.GIEL=1;
RCONbits.IPEN=1;
INTCON2bits.TMR0IP=0;
TMR0H=0xC2;
TMR0L=0xF7;
T0CON=0b100000101;
INTCON=0b11100000;
if(control=1)
{
switch(start)
{
case 0: 
		first=0;
		middle=0;
		last=0;
        break;


case 1:
		first=1;
		middle=0;
		last=0;
		break;
case 2:
		first=0;
		middle=1;
		last=0;
		break;


case 3:
		first=1;
		middle=1;
		last=0;
		break;


case 4:
		first=0;
		middle=0;
		last=1;
		break;


case 5:
		first=1;
		middle=0;
		last=1;
		break;


case 6:
		first=0;
		middle=1;
		last=1;
		break;


case 7:
		first=1;
		middle=1;
		last=1;
		break;


default:
		first=0;
		middle=0;
		last=0;






}






 switch(end){


case 0:
		first1=0;
		middle1=0;
		last1=0;
		break;


case 1:
		first1=1;
		middle1=0;
		last1=0;
		break;


case 2:
		first1=0;
		middle1=1;
		last1=0;
		break;


case 3:
		first1=1;
		middle1=1;
		last1=0;
		break;


case 4:
		first1=0;
		middle1=0;
		last1=1;
		break;


case 5:
		first1=1;
		middle1=0;
		last1=1;
		break;


case 6:
		first1=0;
		middle1=1;
		last1=1;
		break;


case 7:
		first1=1;
		middle1=1;
		last1=1;
		break;
	
default:
		first1=0;
		middle1=0;
		last1=0;












		}


}






}

I've tried to use the other method which require only rand() and srand function. I'm not sure how to seed it so 1 of the 7-segment display odds number while the other display even numbers.

OK - First thing is first


You need to set your config bits -> This sets up thing like the oscillator, watchdog timer - Things that if not set up properly, will make your PIC seem like it is doing random things. Learning how to do this should be your priority. An incorrect setting of LVP (low voltage programing) with a floating pin will lead to a reset every time your hand goes near your microprocessor.


It's good to see that you are now declaring 'j' and 'end'. However, you need to declare them as "volatile". To help you avoid the strenuous task of a Google search, here is how you do that:

Code:

volatile char i, j, start, end;

If you don't declare them as volatile, bad things will happen. If you want to learn more about why this is so, have a look on google or gooligum.

Code:

if(control=1)

statement should be

Code:

if(control==1)

You shouldn't be writing to PORTAbits.RAn, but rather LATAbits.LATAn


You're treating main() like it is going to loop forever (like the loop function on the Arduino), but it's not. If you want it to loop, you'll need to use

Code:

while(1){ /* Everything you want to loop */ }

or

Code:

for(;;) { /* Everything you want to loop */ }

It's really a personal choice which one you use.


As a rule with Microcontrollor programming -> Avoid doing anything in an interrupt that isn't necessary. The usual way to do this is by setting up your program like this:


When a timer interrupt happens -> Set a flag (i.e. Set a (volatile) variable's value from 0 to 1)


In your main loop ->

Code:

(pseudo/C)
int main(void)
{
    /* Set up registers/variable values here */


    while(1) /* Loop forever */
    {
        if (flag == 1)
        {
            flag = 0; // (Clear flag here)


            /* Get your random numbers here */


            /* Use your random numbers here */


        }
    }


    return 0;


}