user53592: There is an IO expander PCA9534PW, Arduino UNO. I don’t really understand how I can manage this expander using UNO over I2C.
I found an example, but here is the reading mode.
What I need:
Set the IO0 pin to exit mode,
set the HIGH / LOW level to IO0.
In the datasheet, I just realized that to enter the settings mode - you need to write Wire.write(0x03).
How can I do it?

user13432: You set the pin mode by setting the configuration register. 
Wire.beginTransmission(0x20);
Wire.write(0x03);                   // Configuration Register
Wire.write(0xfe);                   // IO7-IO1 Input, IO0 Output
Wire.endTransmission();

Then write the output port register with HIGH and LOW.
Wire.beginTransmission(0x20);
Wire.write(0x01);                   // Output Port Register
Wire.write(0x01);                   // IO0 HIGH
Wire.endTransmission();
delay(500);
Wire.beginTransmission(0x20);
Wire.write(0x01);                   // Output Port Register
Wire.write(0x00);                   // IO0 LOW
Wire.endTransmission();

But using a library is much easier. See, for instance, https://github.com/alotaiba/PCA9534. 

53592: <p>There is an IO expander <a href="https://datasheet.lcsc.com/szlcsc/NXP-Semicon-PCA9534PW-118_C161197.pdf" rel="nofollow noreferrer">PCA9534PW</a>, Arduino UNO. I don’t really understand how I can manage this expander using UNO over I2C.</p>

<p>I found an <a href="http://diy-scib.org/content/pca9534-io-expander" rel="nofollow noreferrer">example</a>, but here is the reading mode.</p>

<p>What I need:
Set the IO0 pin to exit mode,
set the HIGH / LOW level to IO0.</p>

<p>In the datasheet, I just realized that to enter the settings mode - you need to write Wire.write(0x03).
How can I do it?</p>
 13432: <p>You set the pin mode by setting the configuration register. </p>

<pre><code>Wire.beginTransmission(0x20);
Wire.write(0x03);                   // Configuration Register
Wire.write(0xfe);                   // IO7-IO1 Input, IO0 Output
Wire.endTransmission();
</code></pre>

<p>Then write the output port register with HIGH and LOW.</p>

<pre><code>Wire.beginTransmission(0x20);
Wire.write(0x01);                   // Output Port Register
Wire.write(0x01);                   // IO0 HIGH
Wire.endTransmission();
delay(500);
Wire.beginTransmission(0x20);
Wire.write(0x01);                   // Output Port Register
Wire.write(0x00);                   // IO0 LOW
Wire.endTransmission();
</code></pre>

<p>But using a library is much easier. See, for instance, <a href="https://github.com/alotaiba/PCA9534" rel="nofollow noreferrer">https://github.com/alotaiba/PCA9534</a>. </p>
