USART vs. UART: Key Differences Every Embedded Engineer Should Know
UART is a basic serial hardware block that shifts bits in and out using only start, data, and stop bits. USART is UART’s smarter sibling: the same core plus clock line and synchronous mode, letting it act like SPI or even LIN when commanded.
Engineers grab “UART” for quick printf debug, then later need higher speeds or multi-protocol support and discover their MCU actually has a USART. The datasheet hides the distinction in footnotes, so the names blur until a late-night scope trace screams “I need a clock!”
Key Differences
UART: asynchronous only, fixed baud, two wires (TX/RX). USART: adds synchronous mode with external clock, master/slave SPI, automatic baud, and hardware flow-control. USART reuses UART registers, so code looks identical until you toggle the “sync” bit.
Which One Should You Choose?
Stick with UART for simple console or GPS streams. Pick USART when you need >1 Mbps, want to daisy-chain sensors via SPI, or plan to reuse pins for multiple protocols without rewiring. Silicon cost is zero—MCUs ship both.
Can I turn a UART into USART in software?
No. Clock generation and frame sync need dedicated hardware; bit-banging tops out at low speeds and hogs CPU.
Do all STM32 chips have USART?
Most do, but budget lines like STM32F0 may offer only UART on low-pin devices—check the reference manual table.
Does using USART increase power draw?
Only when synchronous mode or higher clocks are active; in pure asynchronous mode the consumption equals UART.