Go Down

#### bmagigr

##### Jul 01, 2011, 11:53 pmLast Edit: Jul 01, 2011, 11:55 pm by bmagigr Reason: 1
Hello to everybody First of all I apologise for my bad english
I have a question about the  use of digitalWrite
I have a matrix led and i work with this code (Which is work fine)
------------------------------------------------------------------------------------------
Code: [Select]
`int delayTime= 80;        // 1mS increments before next LEDint delayStep;int ledPin, col, row ;void setup()               // run once, when the sketch starts{for (ledPin=2; ledPin <=12; ledPin++)   // Standard setup for LMP{ pinMode(ledPin, OUTPUT);             // sets the digital pin as outputdigitalWrite(ledPin,(ledPin <=7)) ;     // and sets all OFF}}void loop()                                     // run over and over again/* Map PORTB == D8:D13   PORTD == D0:D7   Our output: col::D7:D2   (8-col) -ve (LOW)   while row::D8:D13 +ve   (row+7) +ve (HIGH)*/{for (row=1; row <=5; row++) {                                            // Vertical: left to rightdigitalWrite(row + 7,HIGH);    // Enable entire ROWfor (col=1; col <=6; col++) {                                           // then one pixel per coldigitalWrite(8- col,LOW);      // gets turned ondelay(delayTime);                 // for a momentdigitalWrite(8- col,HIGH);     // then OFF before next one}                            digitalWrite(row + 7, LOW);   // We're done with this row}.........................`
------------------------------------------------------------------------------------------------------------

I learn in arduino reference quide that the syntax of digitalWrite is digitalWrite (pin, value)
The value is possible to be HIGH or LOW
But in the above code the value is numeric (if understand well)

1st question : What value take the expression digitalWrite(ledPin,(ledPin <=7)
i suppose that take every cycle of "if" the value
1st cycle > digitalWrite(1, 1)
2nd cycle > digitalWrite(2, 2)
3nd cycle > digitalWrite(3, 3)
4th cycle > digitalWrite(4, 4)
5th cycle > digitalWrite(5, 5)
6th cycle > digitalWrite(6, 6)
7th cycle > digitalWrite(7, 7)
and after in 8th cycle what?

2nd queston : When the value is numeric the pin is HIGH or LOW?

The above code is from http://www.instructables.com/id/Build-a-low-cost-scrolling-LED-display-for-your-A/step6/A-test-sketch/

Thanks
babis

#### AWOL

#1
##### Jul 01, 2011, 11:59 pm
Quote
What value take the expression digitalWrite(ledPin,(ledPin <=7)

If ledPin <= 7 then the value written is HIGH, otherwise it is LOW.
The value of HIGH is 1, the value of LOW is 0 (zero)
So, if ledPin is 4
digitalWrite(4, 1);
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.

#2