Comparison of Serial Interfaces

Feature	SPI	I2C	USB	USART	UART
Full form	Serial Peripheral Interface	Inter-Integrated Circuit	Universal Serial Bus	Universal Synchronous/Asynchronous Receiver Transmitter	Universal Asynchronous Receiver Transmitter
Lines	4 (MOSI, MISO, SCK, CS)	2 (SDA, SCL)	4 (VBUS, D+, D-, GND)	TX, RX (+ XCK clock in sync mode)	2 (TX, RX) + GND
Clock	Synchronous	Synchronous	Embedded in data	Sync or async	Asynchronous (baud rate)
Speed	Up to tens of Mbps	100 kbps, 400 kbps, 3.4 Mbps	12 Mbps (USB 1.1), 480 Mbps (USB 2.0) and higher	Up to a few Mbps	9600 to 115200 bps typical
Topology	Master with many slaves	Multi-master, multi-slave	Host with hubs and devices	Point to point	Point to point
Distance	Short (on PCB)	Short (on PCB)	Up to 5 m	Short to medium	Short (RS-232 up to 15 m)
Typical use	ADC, SD card, display	EEPROM, RTC, sensors	PC connection, data loggers	Microcontroller to PC, modems	GPS, Bluetooth modules, debug console

Key notes

• SPI is fastest for chip-to-chip links but uses more pins.
• I2C needs only two wires and supports addressing; pull-up resistors are required.
• USB is plug-and-play with power supply and standard drivers.
• UART needs no clock; both sides must use the same baud rate, format 8N1.
• USART can work as UART or with a shared clock for synchronous mode.

Exam tip

A table covering lines, speed and use is exactly what the question asks.