11.1 TXD,RXD Pin Configuration

When the TXEN,RXEN bit of the UCSRnB register is set, the TXD,RXD pin will be selected. When the USART Receiver is enabled, the RXD pin is configured as an input regardless of the value of the DDxn bit and the RXD pin pull-up can still be controlled by the PORTxn bit. When the USART Transmitter is enabled, the TXD pin is configured as an output regardless of the value of the DDxn bit.

Figure 11-1. USART Control and Status Register n

Bit 4 – RXEN: Receiver Enable

Writing this bit to one enables the USART Receiver. The Receiver will override normal port operation for the RxDn pin when enabled.

Bit 3 – TXEN: Transmitter Enable

Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port operation for the TxDn pin when enabled.