NRF52811-QCAA-R datasheet(381/444 Pages) NORDIC

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Peripherals

6.27.1 Functional description

Listed here are the main features of UART.

The UART implements support for the following features:

• Full-duplex operation

• Automatic flow control

• Parity checking and generation for the 9th data bit

As illustrated in UART configuration on page 380, the UART uses the TXD and RXD registers directly to

transmit and receive data. The UART uses one stop bit.

Note: External crystal oscillator must be enabled to obtain sufficient clock accuracy for stable

communication. See CLOCK — Clock control on page 61 for more information.

6.27.2 Pin configuration

The different signals RXD, CTS (Clear To Send, active low), RTS (Request To Send, active low), and TXD

associated with the UART are mapped to physical pins according to the configuration specified in the

PSEL.RXD, PSEL.CTS, PSEL.RTS, and PSEL.TXD registers respectively.

If the CONNECT field of a PSEL.xxx register is set to Disconnected, the associated UART signal will not

be connected to any physical pin. The PSEL.RXD, PSEL.CTS, PSEL.RTS, and PSEL.TXD registers and their

configurations are only used as long as the UART is enabled, and retained only for the duration the device

is in ON mode. PSEL.RXD, PSEL.CTS, PSEL.RTS and PSEL.TXD must only be configured when the UART is

disabled.

To secure correct signal levels on the pins by the UART when the system is in OFF mode, the pins must be

configured in the GPIO peripheral as described in Pin configuration on page 381.

Only one peripheral can be assigned to drive a particular GPIO pin at a time. Failing to do so may result in

unpredictable behavior.

UART pin

Direction

Output value

RXD

Input

Not applicable

CTS

Input

Not applicable

RTS

Output

TXD

Output

Table 112: GPIO configuration

6.27.3 Shared resources

The UART shares registers and other resources with other peripherals that have the same ID as the UART.

Therefore, you must disable all peripherals that have the same ID as the UART before the UART can be

configured and used. Disabling a peripheral that has the same ID as the UART will not reset any of the

registers that are shared with the UART. It is therefore important to configure all relevant UART registers

explicitly to ensure that it operates correctly.

See the Instantiation table in Instantiation on page 18 for details on peripherals and their IDs.

6.27.4 Transmission

A UART transmission sequence is started by triggering the STARTTX task.

Bytes are transmitted by writing to the TXD register. When a byte has been successfully transmitted the

UART will generate a TXDRDY event after which a new byte can be written to the TXD register. A UART

transmission sequence is stopped immediately by triggering the STOPTX task.

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