user38812: How to send data (Hello World) from Arduino Uno to a PC using USB to TTL/UART (PL2303 4 wires)? Why do I need to press the reset button to upload a program using PL2303?

user4143: 
How to send data(Hello World) from Arduino Uno to PC using USB to TTL/UART(PL2303 4 wires)? 

Serial.print("Hello World");

That is, assuming it's connected to pins 0/1. Otherwise you would have to use SoftwareSerial.

why I need to press the reset button during upload a program using PL2303?

Because it lacks a DTR signal to press the reset button for you (resetting runs the bootloader).

38812: <p>How to send data (Hello World) from Arduino Uno to a PC using USB to TTL/UART (PL2303 4 wires)? Why do I need to press the reset button to upload a program using PL2303?</p>
 4143: <blockquote>
  <p>How to send data(Hello World) from Arduino Uno to PC using USB to TTL/UART(PL2303 4 wires)? </p>
</blockquote>

<pre><code>Serial.print("Hello World");
</code></pre>

<p>That is, assuming it's connected to pins 0/1. Otherwise you would have to use <code>SoftwareSerial</code>.</p>

<blockquote>
  <p>why I need to press the reset button during upload a program using PL2303?</p>
</blockquote>

<p>Because it lacks a DTR signal to press the reset button for you (resetting runs the bootloader).</p>
