Basic interrupt handling in MC9S12DT256B

Aditya — Tue, 10 Mar 2009 07:36:24 GMT

Hello, I'm new to microprocessors and I just began writing interrupt handling for MC9S12DT256B. I contacted freescale and with their assistance, I was able to manage to generate my code for handling interrupts. (with a lot of mistakes though )

My requirement:- The aim is to generate external interrupts on pins 0 and 1 of PORT P of MC9S12DT256B. The figure is shown in the attachment. The outputs of 2 NAND gates (Q and Q^) are given as inputs to pins 0 and 1 of PORT P respectively (so if 1 is high, the other is obviously low). So if the switch is pressed, say interrupt was generated on pin 1 and vice versa. So if pin 1 of PORT P interrupts, I want LED 2 to flash up and if pin 0 interrupts, I want LED 1 to flash up. In my code, I am printing character 'c' on the LCD and I just wanted to make sure that when an interrupt occurs, I show some way that I'll be able to handle it and for the same sake, I tried to stop the printing of 'c' temporarily and show the LED that was lit and resume printing 'c' after a few seconds to ensure that the interrupt was handled correctly. I'm even displaying my source code beneath, kindly help me with your expertise. This is my source code :-

#include <hidef.h>
#include <mc9s12dt256.h>
#include "pbs12dslk.h"
#include "lcd.h"
#include "SCI.h"
#pragma LINK_INFO DERIVATIVE "mc9s12dt256"

/* I think I'm handling the interrupts here */

#pragma CODE_SEG NON_BANKED

interrupt 38 void my_interrupt(void)
   {
   if((PIFP & 0x01) > 0) // if interrupt occurs on pin 0
    {
      PBMCUSLK_LED1 = 1;
      PBMCUSLK_LED2 = 0;
      PIFP = 0x01; // clearing the flag register
    }
   else if((PIFP & 0x02) > 0) // if interrupt occurs on pin 1
    {
    PBMCUSLK_LED1 = 0;
    PBMCUSLK_LED2 = 1;
    PIFP = 0x02; // clearing the flag register
    }
return;
   }

#pragma CODE_SEG DEFAULT

/* The main code starts here */

int main()
{
   unsigned char cha='c';
   unsigned char *p;
   int i,j;
   p=&cha;

   LCDInit();
   INIT_PBMCUSLK_LEDs;

   DDRP = 0x00; // Using all the pins of PORT P as input
   PERP = 0x03; //
   PPSP = 0x03; // pins 0 and 1 set to be pulled down and interrupt occurs on rising edge
   PIEP = 0x03; // pins 0 and 1 set to enable the interrupts

   EnableInterrupts;   // This is the part that I'm confused of, will saying EnableInterrupts; take me to the ISR mentioned above?

   while(1)
   {
    LCDClearDisplay();
    LCDPutString(p);
   }

   DisableInterrupts;

   return 0;
}

Re: Basic interrupt handling in MC9S12DT256B

Aditya — Tue, 10 Mar 2009 22:52:45 GMT

I just made a correction to the interrupt intialization, the vector # must be 56 in decimal (since it is 38 hexa). Even then, my code never enters into the interrupt routine.

Change made:- interrupt 0x38 void my_interrupt(void) instead of

interrupt 38 void my_interrupt(void)

topic Re: Basic interrupt handling in MC9S12DT256B in S12 / MagniV Microcontrollers

Basic interrupt handling in MC9S12DT256B

Re: Basic interrupt handling in MC9S12DT256B