Support » Pololu Wixel User’s Guide » 5. Connecting Your Wixels »
5.b. Connecting a Microcontroller via TTL Serial
<p>If you have loaded a Wixel app that employs one of the Wixel’s two UARTs (such as the <a href="/docs/0J46/9.b">Wireless Serial App</a>), then the Wixel can communicate with another microcontroller via asynchronous, non-inverted TTL serial. Communication between the Wixel and an RS-232 device requires additional hardware.</p>
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<td><table class="picture_with_caption center"><tr><td style="max-width: 253px"><img alt="" class="" data-gallery-pictures="[{"id":"0J3346","caption":"\u003cp\u003eMaking serial connections between a Wixel and a 5V microcontroller.\u003c/p\u003e","url_tiny":"https://a.pololu-files.com/picture/0J3346.98x98.jpg?24a9ef9c991fdbc593a0fa9f2e8c3b83","url_medium":"https://a.pololu-files.com/picture/0J3346.600x480.jpg?24a9ef9c991fdbc593a0fa9f2e8c3b83","url_full":"https://a.pololu-files.com/picture/0J3346.1200.png?24a9ef9c991fdbc593a0fa9f2e8c3b83","longest_side":253}]" data-picture-id="0J3346" data-picture-longest_side="253" src="https://a.pololu-files.com/picture/0J3346.253.png?24a9ef9c991fdbc593a0fa9f2e8c3b83" /></td></tr><tr><th style="max-width: 253px"><p>Making serial connections between a Wixel and a 5V microcontroller.</p></th></tr></table></td>
<td><table class="picture_with_caption center"><tr><td style="max-width: 253px"><img alt="" class="" data-gallery-pictures="[{"id":"0J3347","caption":"\u003cp\u003eMaking serial connections between a Wixel and a 3.3V microcontroller.\u003c/p\u003e","url_tiny":"https://a.pololu-files.com/picture/0J3347.98x98.jpg?9c07f4fa25b136fb5506b74498c286f0","url_medium":"https://a.pololu-files.com/picture/0J3347.600x480.jpg?9c07f4fa25b136fb5506b74498c286f0","url_full":"https://a.pololu-files.com/picture/0J3347.1200.png?9c07f4fa25b136fb5506b74498c286f0","longest_side":253}]" data-picture-id="0J3347" data-picture-longest_side="253" src="https://a.pololu-files.com/picture/0J3347.253.png?9c07f4fa25b136fb5506b74498c286f0" /></td></tr><tr><th style="max-width: 253px"><p>Making serial connections between a Wixel and a 3.3V microcontroller.</p></th></tr></table></td>
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<p>To connect your microcontroller to a Wixel for serial communication, make these connections:</p>
<ul>
<li><strong>GND:</strong> Connect the ground (also known as GND or VSS) of your microcontroller to one of the GND pins on the Wixel. This connection is required.</li>
<li><strong>TX:</strong> If you want the microcontroller to be able to receive serial bytes from the Wixel, connect the Wixel’s TX line to the microcontroller’s RX line.</li>
<li><strong>RX:</strong> If you want your microcontroller to be able to send serial bytes to the Wixel, connect the microcontroller’s TX line to the Wixel’s RX line. The Wixel’s RX line is <strong>not</strong> 5 V tolerant. If your microcontroller is running at 5 V (or any voltage significantly above 3.3 V) then you will need to add extra components to ensure that your microcontroller never drives the Wixel’s RX line higher than 3.3 V. A simple voltage divider consisting of 2 resistors as shown in the diagram above will suffice. The Wixel’s RX line has an internal 20 kΩ pull-up resistor.</li>
<li><strong style="text-decoration:overline;">RST</strong><strong>:</strong> If you want the microcontroller to be able to reset the Wixel, then connect the Wixel’s <span style="text-decoration:overline;">RST</span> line to any free general-purpose I/O (GPIO) line on the microcontroller. The microcontroller can drive this line low to reset the Wixel and then stop driving the line to release the Wixel from reset. The Wixel’s <span style="text-decoration:overline;">RST</span> line is <strong>not</strong> 5 V tolerant. If your microcontroller is running at 5 V (or any voltage significantly above 3.3 V) then you must avoid driving the Wixel’s RST line high. If that is not possible, then you could put a diode between the Wixel’s <span style="text-decoration:overline;">RST</span> line and the microcontroller’s GPIO to prevent current from flowing in the wrong direction (from the GPIO). The connection to <span style="text-decoration:overline;">RST</span> is optional and not required for sending or receiving data.</li>
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<p>Please refer to the documentation of your specific Wixel app to determine the location of the TX pin(s) and RX pin(s).</p>
<p class="note_warning"><strong>Note:</strong> The Wixel does <strong>not</strong> support the RS-232 voltage levels typically used by DB9 serial ports. The Wixel’s I/O lines, including the RX and TX lines, operate on voltages between 0 and 3.3 V are <strong>not</strong> 5 V tolerant. To connect the Wixel to an RS-232 serial signal, you will need additional level-shifting and inverting hardware like the <a href="/product/126">Pololu 23201a serial adapter</a> (RS-232 serial is inverted; the Wixel’s serial interface expects non-inverted serial).</p>