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Flashing LED's beyond on and off

 
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Neutone



Joined: 08 Sep 2003
Posts: 839
Location: Houston

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Flashing LED's beyond on and off
PostPosted: Fri Dec 08, 2006 3:29 pm     Reply with quote

It's probably one of the first things most people learn to do with code on an embedded processor. A lot of circuits don't have much of a way to display information other than a single LED. A single LED can have 5 completely distinct visual states.
Off
Flash 1/2 second on/off
Strobe 1/8 second on/off
Flash/Strobe
On


I like to have the LED off only when the circuit has no power. That means I only need to control 4 states when power is on. I usually have 2 bits that carry some kind of information. Assume you want to show when an alarm occurs and when some process is happening.
Code:

Int16    LED_period=0;
Int1     LED_Alarm=0;
Int1     LED_Process=0;

Void     Service_LED(Void)
{  if(LED_period)
   {  LED_period--;
   }
   Else
   {  LED_period=4000;
   }
   Status_LED=(bit_test(LED_period,8) || !LED_Alarm)
      && (bit_test(LED_period,6) || !LED_Process);
}

The service routine needs to be called every mS as written. The rate can be changed by changing the bits tested in the bit_test. The alarm and process bits are modified elsewhere. This compiles to a very small size and has very low execution time as well. This can be reduced if you already have a mSecond variable that can be used in the place of LED_period.
Storic



Joined: 03 Dec 2005
Posts: 182
Location: Australia SA

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PostPosted: Sat Dec 09, 2006 4:07 pm     Reply with quote

With the Status_LED,I am not sure of the bit
is it a variable or the output bit (led)
below I assigned Status_LED as a bit 2 of Port B

Code:
#byte State_L = 0xF81 // PORT B; PORT A = 0xF80
#bit Status_LED = State_L.2


my question is How did you assigned Status_LED, I will get to try the above code within the next few weeks.

Andrew
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Neutone



Joined: 08 Sep 2003
Posts: 839
Location: Houston

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PostPosted: Sun Dec 10, 2006 12:51 am     Reply with quote

Did you set the pin as an output?
This example code flashes an LED that lights up when the output on pin B5 goes low. I ran this on the CCS developers kit for PIC18F452.
Code:
#include <18F452.h>
#fuses NOWDT,WDT128,HS, NOOSCSEN, BROWNOUT, BORV20, PUT, STVREN, NOLVP
#use delay(clock=20000000)

#byte    Port_B = 0xF8A
#bit     Status_LED = Port_B.5

Int16    mS_Counter;
Int16    Second_Counter;
Int1     LED_Alarm;
Int1     LED_Process;

Void     Service_LED(Void)
{  Status_LED=!((bit_test(mS_Counter,8) || !LED_Alarm)
      && (bit_test(mS_Counter,5) || !LED_Process));
}

#int_TIMER2
TIMER2_isr()
{  mS_Counter++;
   if(mS_Counter>999)
   {  mS_Counter=0;
      Second_Counter++;
   }
}

void main()
{  setup_timer_2(T2_DIV_BY_4,249,5);
   enable_interrupts(INT_TIMER2);
   enable_interrupts(GLOBAL);

   SET_TRIS_B(0b11001111);
   while(1)
   {  Service_LED();
      LED_Alarm=bit_test(Second_Counter,3);     // For lack of a real alarm just turn on and off
      LED_Process=bit_test(Second_Counter,4);   // For lack of a real process just turn on and off
   }
}
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