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Timer Interrupt Loading for PIC and CCS C

 
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glenjoy



Joined: 18 Oct 2004
Posts: 21

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Timer Interrupt Loading for PIC and CCS C
PostPosted: Wed Apr 13, 2005 10:32 pm     Reply with quote
I want to create a device that will Turn OFF a device after a preset time, the preset time can be incremented by 30 minutes at the selector, running time selection or ON times selection will be from 30 min. to 9.5 hours with selection increments of 30 min.

Now how can I use the timer to time out the PIC micro after my preset ON time and which timer to use, I do not want to use delay_ms command because while waiting for the time to expire I am displaying the preset time.

Thanks.

PS. If you are quite confused, just tell me.
Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Thu Apr 14, 2005 6:35 am     Reply with quote
Pick a timer. It doesn't really matter which one. Take a look (search the forum) at the code that keeps track of time (RTC). You are going to have to setup the timer to count a smaller unit of time, say seconds or even smaller, maybe tenths of seconds.

Here is a snippet that is called every milisecond. It is not my acutal code but a version that I edited in an effort to make it a little clearer:
Code:
void Relay_Timers(void)
{
  static uint8_t  secs_count   = 0; /* Used to count seconds */
  static uint8_t  tenths_count = 0; /* Used to count tenths of seconds */
  uint8_t         count;

  /* Handle the warn and timeouts. These are in seconds */
  tenths_count++;

  // 100 miliseconds is a tenth
  if (tenths_count >= 100)
  {
    tenths_count = 0;
    secs_count++;

    // 10 tenths is a second
    if (secs_count >= 10)
    {
      secs_count = 0;
      for (count=0; count < MAX_RELAYS; count++)
      {
        if (RelayTimers[count].timeout)
        {
          if (--RelayTimers[count].timeout == 0)
            Relay_Activate(count, 0, 0, 0);
          else if (RelayTimers[count].timeout == RelayTimers[count].warn)
            Relay_Warn(count);
        }
      }
    }
  }
}
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