user59006: I'm using Arduino MKR GSM 1400. I know this board uses Atmel SAMD21 and SAMD21 support half duplex (USART with full-duplex and single-wire half-duplex configuration). My question is, How Can I configure one of the SERCOMs to use it as Half-Duplex (Use one pin for rx and tx)?

user37622: 
Up to six Serial Communication Interfaces (SERCOM), each configurable
to operate as either:

USART with full-duplex and single-wire half-duplex configuration
I2C up to 3.4 MHz
SPI
LIN slave


It is an error in the overview of the SAM D21 features in the datasheet. The SERCOM is half-duplex for I2C. USART can't be configured half-duplex.
see Application Note about SERCOM configuration

1 Introduction to Serial Communication Interfaces (USART, I2C, and
SPI)
... The exchange of data can be half-duplex or fullduplex depending on
the serial module specification. ...
1.1 USART
... It is full-duplex in operation. ...
1.2 I2C
... It is half-duplex in communication. ...


59006: <p>I'm using Arduino MKR GSM 1400. I know this board uses Atmel SAMD21 and SAMD21 support half duplex (USART with full-duplex and single-wire half-duplex configuration). My question is, How Can I configure one of the SERCOMs to use it as Half-Duplex (Use one pin for rx and tx)?</p>
 37622: <blockquote>
<p>Up to six Serial Communication Interfaces (SERCOM), each configurable
to operate as either:</p>
<ul>
<li>USART with full-duplex and single-wire half-duplex configuration</li>
<li>I2C up to 3.4 MHz</li>
<li>SPI</li>
<li>LIN slave</li>
</ul>
</blockquote>
<p>It is an error in the overview of the SAM D21 features in the datasheet. The SERCOM is half-duplex for I2C. USART can't be configured half-duplex.</p>
<p>see <a href="https://www.microchip.com/wwwAppNotes/AppNotes.aspx?appnote=en590861" rel="nofollow noreferrer">Application Note about SERCOM configuration</a></p>
<blockquote>
<p>1 Introduction to Serial Communication Interfaces (USART, I2C, and
SPI)</p>
<p>... The exchange of data can be half-duplex or fullduplex depending on
the serial module specification. ...</p>
<p>1.1 USART</p>
<p>... It is full-duplex in operation. ...</p>
<p>1.2 I2C</p>
<p>... It is half-duplex in communication. ...</p>
</blockquote>
