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Toggling LED

Matt Werner

Hello all

I am quite new to Keil STR9 Series. I was just learning the whole thing by going through and trying some small examples with it.
I want to know how to control just one LED ( say 7.0) to blink at a time.

   while (1)
         {
            for (n = 0x01; n <= 0xFF; n <<= 1)
            {
               GPIO7->DR[0x3FC] = n;
            }
         }

This piece of code turns on the all 8 LEDS at the same time. How can i blink just one LED (7.0) every 1 second?

Thanks

Parents Reply Children
  • 0 in reply to ImPer Westermark

    I looked for it . but couldnt get clear expalanation.
    There is an example code which do waiting

    void wait (void)  {                       /* Wait function                    */
  int d;

  d = AD_last;                            /* Read AD_last value               */
  if (d != AD_last)                       /* Make sure that AD interrupt did  */
    d = AD_last;                          /* not interfere with value reading */

  d *= 500;
  d += 50000;                             /* Scale analog value for delay     */
                                          /* lower value -> longer delay      */
  while (d--);                            /* Only to delay for LED flashes    */
}

    I tried to modify this, using like this in my case.

    
void wait (void)
{                                       /* Wait function                    */
  int d= 1000;
  while (d--);                            /* Only to delay for LED flashes    */
}


while(1) {
           for (n = 0x01; n <= 0x1; n <<= 1)
            {
               GPIO7->DR[0x3FC] = n;
               wait();_
           }

    But nothing happens

  • 0 in reply to Matt Werner

    So your first reference to wait(ms) was just a random chance? Not based on you having found such a function in any runtime library documentation for any runtime library you are using? Is that a good way to write code?

    Your next attempt - did you test to search about delays on this forum? If you did, you would have found quite a number of discussions about the problems with using busy-loops in C without binding the delay time to some real hardware property.

    Another thing - how long do you think your puny 1000-step delay takes? Do you really expect that your eye will be able to see any result of such a short delay?

    Yet another thing - if you want to blink a LED, you need to repeatedly do:
    - Turn on the LED.
    - Wait for x milliseconds.
    - Turn off the LED.
    - Wait for 1000-x milliseconds.

    Based on the documentation for your processor:
    - Do you see code both for turning on and for turning off any LED?
    - Does the processor documentation suggest that a 1000-step for loop would be a suitable delay?

    Note that turn on/turn off can be handled by the same primitive, if you use a primitive that toggles the pin state.