The short answer is yes, UART (Universal Asynchronous Receiver/Transmitter) is a full duplex serial communication protocol. This means UART can transmit and receive data simultaneously on a single communication line.
What is UART?
UART stands for Universal Asynchronous Receiver/Transmitter. It is a hardware communication protocol that allows serial data transfer between two devices. The UART protocol handles asynchronous serial communication by synchronizing the transmitting and receiving devices using start and stop bits flanking the data frame being transferred.
Some key characteristics of UART communication:
- Asynchronous – There is no common clock signal between the transmitting and receiving device. The synchronization is achieved using start and stop bits.
- Full duplex – Transmission in both directions simultaneously.
- Serial communication – Data is sent one bit at a time sequentially over a single communication line.
- Simplex – Only one wire is needed for each direction of data transfer (one wire for TX, one for RX).
UART Hardware Interface
The UART hardware interface consists of a transmitter block, a receiver block and a communication line between the two devices.
The transmitter block converts the parallel data from the device into a serial stream by appending start, stop and parity bits. This serialized stream is sent out through the TX pin.
The receiver block at the other end reads in the serial data stream through its RX pin. It then extracts the actual data frame by stripping away the start, stop and parity bits. This data is converted back into parallel data for the receiving device.
The communication line consists of two wires – one for TX and one for RX. This allows full duplex communication where data can be transmitted and received at the same time.
UART Frame Format
The UART frame format consists of the following components:
- Start bit – Indicates the beginning of a new data frame. It is normally kept low.
- Data bits – The actual data being transferred, usually 5-8 bits.
- Parity bit – Optional error checking on the data bits using even/odd parity.
- Stop bit(s) – Indicates the end of the data frame. Normally kept high.
For example, a common UART frame would look like:
Start Bit | 8 Data Bits | Parity Bit | Stop Bit
The start and stop bits are used by the receiver to identify valid data frames being sent by the transmitter. This allows synchronization without a shared clock between the devices.
UART Communication Process
The process of transferring data between two UART devices works as follows:
- Transmitting device checks if transmission line is free.
- Start bit is sent to signal start of data frame.
- Data bits (5-8 bits) are sent sequentially.
- Optional parity bit sent for error checking.
- Stop bit(s) are sent to signal end of data frame.
- Receiving device detects start bit and synchronizes to transmitter’s bit rate.
- Data bits are read by receiver until stop bit is detected.
- Receiver assembles the extracted data bits into a data frame.
- Optional parity checking done to detect errors.
- Data frame is converted from serial to parallel if required.
This process allows asynchronous serial transfer of data frames between two UARTs in full duplex mode.
UART Full Duplex Capability
UART is able to transmit and receive data at the same time by using separate TX and RX lines. This is known as full duplex communication.
Technically, UART is considered a “half-duplex asynchronous system” because both devices take turns to send or receive data. However, the switching between transmit and receive modes happens so rapidly that it can be considered simultaneous for all practical purposes.
Some key points about UART full duplex capability:
- Separate TX and RX lines allow transmission in both directions.
- Transmitter and receiver can operate independently.
- No collisions between outgoing and incoming data frames.
- Full duplex provides higher throughput than half duplex.
- Ideal for low cost communication between two devices.
Uses that benefit from UART full duplex capability:
- Microcontroller to PC communication (USB-UART bridges)
- On-chip debugging between debugger and MCU
- Chip-to-chip communication in embedded systems
- Data transfer between modules in a device
- Console interfaces (Telnet, SSH)
Implementing Full Duplex UART
On the hardware side, implementing full duplex UART communication requires:
- UART controller block with separate TX and RX sub-blocks.
- TX and RX pins for interfacing.
- FIFO buffers to hold received and transmitted data.
- Registers, timers, and interrupt control.
- Oversampling for high baud rates.
- Optional error detection modules.
For software UART implementations, the transmit and receive logic needs to be programmed to work independently. This allows received data to be buffered while transmission is ongoing.
Device drivers should be written accordingly to handle concurrent read and write requests by using interrupts, DMA, buffers etc. This ensures the UART hardware capability is translated into full duplex communication at the software level.
Advantages of UART Full Duplex
Some of the key advantages of having full duplex capability in UART communication are:
- Higher throughput – Data can be sent and received simultaneously.
- Real-time communication – Important for control systems and real-time data transfer.
- Simpler communication – No turn taking required between devices.
- Flexible configurations – Each device can act as transmitter or receiver independently.
- Minimal wiring – Only 2 wires can provide bi-directional communication.
- Ubiquitous support – Most microcontrollers, CPUs have UART interface.
In summary, UART’s full duplex capability along with its asynchronous serial communication make it one of the most popular and widely used interfaces for low cost embedded communication.
