How make a delay?

[PedroM]

Hello,

I´m beginner  programmer with MC9RS08KA in C, and would like to help to create a delay of 700ms. e.g. After press a button, one led turn on after 700ms. I knew the function delay_ms() used in PICs, but I don't know how make with codewarrior. Anyone know?

tks.

[bigmac]

Hello, and welcome to the forum.

The 'RS08KA8 device has two timer modules, a MTIM and a TPM.  Either could be used to generate a delay of 700ms.  I will explain a possible approach using the MTIM module.

Since the 'RS devices do not have a proper interrupt capability, you will need to poll for the occurrence of MTIM overflow.  Depending on your requirements, you could generate the delay in one 700ms increment, or alternatively in a number of smaller increments of perhaps 10ms each, and to count the number of overflows for the required delay period.  If you have a number of different intervals to generate, and maybe run concurrently, the second method would be the preferred one.

You would need to select the fixed frequency clock source to obtain a sufficiently long timing period, i.e. a frequency between the limits 15.625kHz and 19.531kHz, depending on the internal reference clock trim.  This is the internal reference frequency divided by two.  It is then a matter of setting the prescale value and the MTIMMOD value to obtain the required delay.

For example, a trim setting for a fixed frequency clock of 15.625kHz, a prescale setting of 64, and MTIMMOD = 170 would produce a delay in the vicinity of 700ms.  The delay formula is PS*(MTIMMOD + 1) / FFCLK.

Regards,

Mac

[PedroM]

Hello,

Tkank very much, for quickily answers and for help. Until i can make one increments as code bellow? This correct?

 if(SIP1_MTIM1){    //timer 20ms

      q++;

      if(q == 500){    //when it reaches x ms

          LAMP = 1;     //turn off  lamp

          q = 0;

      }

      else {

         LAMP = 0;

      }

      }

      (void) MTIM1SC_TOF;

          MTIM1SC_TOF = 0; 

[bigmac]

Hello Pedro,

I think that it would be a good idea for your delay processing to be generally applicable, and not specifically for the timing of a LED.  To do this, I think that you would need two functions - one function to setup the delay in the first instance, and a second function that could be periodically polled to test for a delay timeout condition.  Both these functions can then be called from your main loop to meet the requirements of your application.

// Global variable:unsigned int q;void set_delay( unsigned int x){   q = x;   MTIMSC = 0x20;  // Counter reset   MTIMSC_TOF = 0; // Clear flag}unsigned int test_timeout( void){   if (MTIMSC_TOF) {      MTIMSC_TOF = 0; // Clear flag
      if (q)  q--;   }   return q;
}

The following code snippet might be used to control the LED.

LAMP = 0;set_delay( 50);         // 1 second delaywhile (test_timeout()); // Wait for timeoutLAMP = 1;

If the COP (watchdog) is enabled, you will also need to clear the COP timer while you wait for timeout to occur.

Regards,

Mac

[Lundin]

The professional way is to use one of the on-chip timers or the RTC (real time clock). You'll have to read about those in the manual.

The hobbyist way is to burn away all CPU capacity in a counting loop with a volatile counter variable. You will have to disassemble the code and count the instructions and their cycles, or alternatively write the function in assembler.

The same for contact debouncing: you will have to debounce the button with a timer, no matter if you are using Freescale or PIC.