Write a short note on: UART and USART

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Accepted Answer

## Short Note: UART and USART

### UART
Universal Asynchronous Receiver Transmitter: a serial link using two lines, TX and RX (plus GND), with **no clock line**. Both ends must use the same **baud rate**.

Frame: 1 start bit (0), 5 to 9 data bits (LSB first), optional parity bit, 1 or 2 stop bits (1).

```mermaid
flowchart LR
  A[Idle line high] --> B[Start bit low]
  B --> C[Data bits D0 to D7]
  C --> D[Parity bit optional]
  D --> E[Stop bit high]
```

### USART
Universal **Synchronous**/Asynchronous Receiver Transmitter: works as a UART, or in synchronous mode with a shared clock (XCK) that allows higher speed and no start/stop bits.

| Point | UART | USART |
|---|---|---|
| Clock | None, baud rate agreed | Optional shared clock |
| Modes | Asynchronous only | Async and sync |
| Speed | Moderate | Higher in sync mode |
| Lines | TX, RX | TX, RX, XCK |

Used with RS-232/RS-485 drivers, GPS, Bluetooth modules and PC serial links.

### Exam tip
Draw the frame format and the UART vs USART table.

Short Note: UART and USART

UART

USART

Exam tip

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