[SOLVED] Possible issue with "digitalWrite".

[abecedarian 330]

MSP-EXP430F5529LP, Energia 11

 

Code:

void setup()
{
  pinMode(GREEN_LED, OUTPUT);
  digitalWrite(GREEN_LED, HIGH);
}

void loop()
{
  delay(500);
  digitalWrite(GREEN_LED, !GREEN_LED);     // toggle green LED
}

... is used, the green LED will light after the sketch is uploaded then turn off, but does not light again.

 

 

But-

void setup()
{
  pinMode(GREEN_LED, OUTPUT);
  digitalWrite(GREEN_LED, HIGH);
}

void loop()
{
  delay(500);
  digitalWrite(GREEN_LED, !digitalRead(GREEN_LED));     // toggle green LED
}

... does cause the LED to toggle.

[abecedarian 330]

Similarly,

void setup()
{
  pinMode(GREEN_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);
  digitalWrite(GREEN_LED, HIGH);
  digitalWrite(RED_LED, !(GREEN_LED));
}

void loop()
{
  delay(500);
  digitalWrite(GREEN_LED, !digitalRead(GREEN_LED));
  digitalWrite(RED_LED, !GREEN_LED);
}

... should cause the red LED to be in the opposite state of the green LED, but it never changes state.

 

But...

void setup()
{
  pinMode(GREEN_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);
  digitalWrite(GREEN_LED, HIGH);
  digitalWrite(RED_LED, LOW);
}

void loop()
{
  delay(500);
  digitalWrite(GREEN_LED, !digitalRead(GREEN_LED));
  digitalWrite(RED_LED, !digitalRead(GREEN_LED));
}

... works as expected.

[reaper7 67]

but word GREEN_LED means "shortcut" to pin number not a pin state (or value),

so !GREEN_LED give you logical negation of value from pins_energia.h

where:

static const uint8_t GREEN_LED = 14;

[abecedarian 330]

I would think that:

digitalWrite(GREEN_LED, !GREEN_LED);

... would assign GREEN_LED, the first parameter of the function, the value represented by the second parameter of the function, as that's what it's supposed to do, no?

[abecedarian 330]

Okay, I get what you mean....

 

GREEN_LED is a 'constant' assigned to a pin, so inverting the constant doesn't invert its state.

 

/me goes back to my location... over here, doing over here things.

[icserny 9]

digitalWrite(GREEN_LED, !digitalRead(GREEN_LED)); // toggle green LED

 

digitalWrite(GREEN_LED, !digitalRead(GREEN_LED));     // toggle green LED

... does cause the LED to toggle.

 

Yes of course. You must first read the digital status of the GREEN_LED pin so that you could negate it.

 

An alternative would be: you can store the status of the GEEN_LEED pin in a RAM variable:

int ledstate;

void setup()
{
  pinMode(GREEN_LED, OUTPUT);
  digitalWrite(GREEN_LED, HIGH);
  ledstate = HIGH;
}

void loop()
{
  delay(500);
  ledstate = !ledstate;                          //toggle status
  digitalWrite(GREEN_LED, ledstate); // update green LED status
}

[abecedarian 330]

Yes, I'm guilty of PUI.

Programming

Under the

Influence.

 

Who spiked my eggnog?

[spirilis 1,265]

Haha in all honesty, that is the sort of "contextual expressiveness" many of us desire in a language but reality always being more mechanistic.

 

Sent from my Galaxy Note II with Tapatalk 4

 

 

[abecedarian 330]

"... reality being more masochistic" is more like it.