user26276: I have an LCD Display HD44780 model and I was reading his datasheets
I saw the it has the functionality to be switched on/off as stated:

Display on/off control: D = 0; Display off // C = 0; Cursor off // B = 0;
  Blinking off

and by continue reading it states:

Then he states again:
Display On/Off Control

D:  The display is on when D is 1 and off when D is 0. When off, the
  display data remains in DDRAM.

But I can't reaaly understand what I fisically need to do, can anyone help me out to better understand?
EDIT:
For better clarify myfinal goal is to completely (power OFF) the LCD screen, I have some NPN transistors and if this would be the best solution, how about the wiring? do I have only to stop suppying VDO?

user13594: Assuming that display is initialized in 8-bit mode: to send command such as "Turn display on/off", 

set RS to LOW first (meaning it is command, not data)
set command bits on DB7-DB0 (in your case it could be 0x08 - DB2/DB1/DB0 all LOW to turn off following: display, cursor and blinking)
make a pulse on EN pin LOW-HIGH-LOW (take a 40uS delay before further communication)


26276: <p>I have an LCD Display HD44780 model and I was reading his <a href="https://i.stack.imgur.com/GLKvp.jpg" rel="nofollow noreferrer">datasheets</a></p>

<p>I saw the it has the functionality to be switched on/off as stated:</p>

<blockquote>
  <p>Display on/off control: D = 0; Display off // C = 0; Cursor off // B = 0;
  Blinking off</p>
</blockquote>

<p>and by continue reading it states:</p>

<p><a href="https://i.stack.imgur.com/GLKvp.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GLKvp.jpg" alt="enter image description here"></a></p>

<p>Then he states again:</p>

<p><strong>Display On/Off Control</strong></p>

<blockquote>
  <p>D:  The display is on when D is 1 and off when D is 0. When off, the
  display data remains in DDRAM.</p>
</blockquote>

<p>But I can't reaaly understand what I fisically need to do, can anyone help me out to better understand?</p>

<p>EDIT:
For better clarify myfinal goal is to completely (power OFF) the LCD screen, I have some NPN transistors and if this would be the best solution, how about the wiring? do I have only to stop suppying VDO?</p>
 13594: <p>Assuming that display is initialized in 8-bit mode: to send command such as "Turn display on/off", </p>

<ul>
<li>set RS to LOW first (meaning it is command, not data)</li>
<li>set command bits on DB7-DB0 (in your case it could be 0x08 - DB2/DB1/DB0 all LOW to turn off following: display, cursor and blinking)</li>
<li>make a pulse on EN pin LOW-HIGH-LOW (take a 40uS delay before further communication)</li>
</ul>
