UART communications require two pins: Receive Data (RX) and Transmit Data (TX):
- RX (Receive Data): RX is the serial data input. Glitch filter and oversampling techniques are used on the receive signal to ensure accurate incoming data.
- TX (Transmit Data): TX is the serial data output. When the transmitter is enabled and no data needs to be transmitted, the TX pin will be held high. In some bidirectional protocols like
ISO7816 Smart card, this pin is also used to receive data.
In hardware flow control mode, the following pins are also used:
- CTS (Clear To Send): when driven high by external signal, this signal blocks the data transmission at the end of the current transfer.
- RTS (Request To Send): when low, this signal indicates that the UART is ready to receive data.