RxD

RxD, short for receive data, is a common label for the data input line used by a device’s serial receiver in asynchronous communication systems. In UART-based interfaces, two primary data lines are typically present: TXD (transmit data) and RXD (receive data). The label appears on circuit diagrams, device pinouts, and software documentation to indicate the direction of data flow relative to the device.

Hardware usage: The RXD line carries serial data from the transmitting device to the receiving device. On a PC with an RS-232 serial port, the PC’s RXD pin receives data from the other device’s TXD. In microcontroller projects that use TTL-level UART, RXD is the input pin to the microcontroller that collects the incoming serial stream; voltage levels depend on the signaling standard, such as TTL/CMOS 0–5V or 0–3.3V, or the higher magnitude RS-232 levels via a level shifter.

Software usage: In software, RXD may denote the receive data buffer or event that fires when new serial data arrives. Serial APIs typically provide reading methods or event handlers for data on the RXD line, abstracting the electrical signaling.

Naming and variants: RXD is often written as RXD or RxD; its counterpart is TXD. Other related signals in serial interfaces include RTS/CTS flow control and DCD, DTR, DSR, and RI status lines.

Note: The exact electrical characteristics and pin assignments for RXD vary by device and standard, so consulting the specific hardware documentation is essential.