UART (Universal Asynchronous Receiver/Transmitter) and I2C (Inter-Integrated Circuit) are two common communication protocols used in embedded systems and IoT devices. The main differences between UART and I2C are:
- UART is asynchronous while I2C is synchronous.
- UART uses 2 wires for communication while I2C uses 2 bi-directional wires.
- UART can operate in full duplex mode whereas I2C can only operate in half duplex mode.
- UART requires more hardware resources than I2C.
- I2C supports multi-master and multi-slave but UART only supports point-to-point communication.
- I2C needs pull up resistors whereas UART does not need them.
- The maximum speed of UART is higher compared to I2C.
- UART communication is less complex than I2C.
What is UART?
UART stands for Universal Asynchronous Receiver/Transmitter. It is a commonly used serial communication protocol that allows full duplex asynchronous communication between two devices. Some key points about UART:
- UART uses 2 wires for communication – RX (Receive) and TX (Transmit).
- It does not share a common clock between the transmitting and receiving devices.
- Devices operate at different baud rates and synchronization happens based on start and stop bits.
- UART can operate in full duplex mode allowing simultaneous communication in both directions.
- Simple interface requiring just 2 wires makes UART hardware easy to implement.
- UARTs are commonly used for serial ports, debugging outputs, and communicating with peripherals like GPS, Bluetooth etc.
What is I2C?
I2C stands for Inter-Integrated Circuit. It is a synchronous serial bus protocol that requires only 2 bidirectional wires for communication. Some key points about I2C:
- I2C uses 2 bidirectional open drain lines – SCL (Serial Clock) and SDA (Serial Data).
- Devices on the I2C bus share a common clock generated by the master.
- I2C supports multi-master and multi-slave unlike UART.
- Start and stop conditions frame the data transfer between devices.
- Only allows half duplex communication as the lines are shared in both directions.
- Pull up resistors are required on SCL and SDA lines.
- I2C is preferred for short distance communication between chips on a single PCB.
Detailed Comparison Between UART and I2C
1. Communication
The primary difference between UART and I2C is the type of communication they support.
- UART supports asynchronous full duplex communication. The transmitting and receiving devices can communicate independently without a shared clock.
- I2C supports synchronous half duplex communication. Devices on the bus share a common clock line generated by the I2C master and take turns to transmit data.
2. Wiring
UART and I2C use different wiring configurations to connect devices.
- UART uses 2 wires – RX and TX for receiving and transmitting data respectively. They operate on different voltage levels.
- I2C uses 2 bidirectional open drain lines – SCL and SDA. Pull-up resistors are required on these lines as they are open drain.
3. Speed
There is a significant difference between the maximum speed supported by UART and I2C.
- UART can operate at maximum baud rates of 1 Mbps or higher depending on the implementation.
- I2C typical speed is 100 kbps to 400 kbps. The maximum speed is 3.4 Mbps for fast mode.
4. Complexity
UART is simpler to implement than I2C in hardware.
- UART just needs a baud rate generator, transmitter, receiver and a few control signals.
- I2C is more complex with clock synchronization, start/stop generation, acknowledgements, arbitration etc.
5. Hardware Overhead
UART requires more hardware resources than I2C.
- UART needs dedicated transmitter and receiver buffers along with control registers.
- I2C just needs a single master module that is shared between multiple slaves. Fewer transmit and receive buffers are needed.
6. Topology
UART and I2C have very different communication topologies.
- UART supports point-to-point communication between two devices only.
- I2C supports multi-master and multi-slave communication on a shared bus. Many ICs can be connected to the same I2C bus.
7. Pull Up Resistors
Pull up resistors are required for I2C but not for UART.
- UART does not require any pull up resistors on the RX and TX lines.
- I2C lines SCL and SDA are open drain so pull ups are required for the bus to operate.
8. Distance
UART can communicate over longer distances than I2C.
- UART can communicate upto 1 KM distance with RS-485 interfaces.
- I2C typically operates over a distance of 1 meter though range can be extended with special ICs.
9. Flow Control
Flow control is inherent in I2C but needs to be implemented separately for UART.
- I2C has built-in flow control using clock stretching and start/stop conditions.
- UART needs flow control protocols like hardware or software handshake to be implemented.
10. Error Handling
I2C has better error checking capabilities compared to UART.
- I2C uses acknowledge bits and CRC to ensure error free transmission.
- UART just has parity and start/stop bits for basic error checking.
Summary
In summary, the main differences between UART and I2C are:
- UART is asynchronous, I2C is synchronous.
- UART uses 2 wires, I2C uses 2 bidirectional wires.
- UART supports full duplex, I2C supports half duplex.
- UART has simpler hardware, I2C has higher hardware overhead.
- UART is point-to-point, I2C supports multi-master and slave.
- I2C needs pull ups, UART does not need them.
- UART has higher maximum speed compared to I2C.
- UART is simpler to implement than I2C.
In conclusion, UART is better suited for asynchronous long distance communication between two devices. I2C is better for short distance communication between multiple devices on a single board.
