Serial communication

Serial communication sends a stream of data in sequence rather than presenting a whole word on multiple parallel wires. A transmitter converts bytes into an ordered signal, while a receiver reconstructs them using agreed timing and format.¹ In asynchronous links, such as a UART, each character commonly has a start bit, a configured number of data bits, an optional parity bit, and one or more stop bits. Synchronous links instead share or recover a clock, allowing continuous frames and often higher efficiency. Duplex describes direction: simplex is one-way, half-duplex alternates direction, and full-duplex permits both directions simultaneously.

Serial signaling may be electrical, optical, or radio-based. The logical data format is separate from the physical layer: identical bytes can travel through copper voltage levels, differential pairs, light pulses, or a wireless carrier.

Serial interfaces differ chiefly in how they provide timing, addressing, electrical compatibility, and error detection. RS-232 commonly serves short point-to-point connections, whereas differential standards such as RS-485 tolerate electrically noisy environments and can support multidrop arrangements. USB combines serial signaling with host-controlled enumeration, device classes, power management, and packetized transfers.² Embedded systems also use SPI for clocked peripheral links and I²C for addressed, two-wire buses.

Framing gives a receiver boundaries and meaning. A frame can contain an address, control field, payload, and check value; protocols such as PPP define octet framing and error-detection procedures for serial links.³ Parity catches some single-bit errors, while checksums and cyclic redundancy checks detect broader classes; retransmission or higher-level recovery is required to correct them.

Serial communication remains central because modest wiring and robust physical links often matter more than maximum raw throughput. Industrial controllers use Modbus over serial lines for polling devices and exchanging register-oriented data.⁴ Vehicles use the Controller Area Network (CAN), in which message identifiers participate in bus arbitration and frames include error-detection mechanisms.⁵ A computer’s console port, a microcontroller’s debugging connection, a barcode scanner, and a satellite telemetry channel may all be serial while using entirely different protocols.

Layering prevents a frequent design error: baud rate, voltage levels, connector wiring, packet format, and application meaning are separate decisions. A USB cable cannot automatically substitute for an RS-232 cable, even though both carry data serially; transceivers, signaling rules, and protocol stacks must be compatible.

Serial links expose several subtle edge cases that are easy to miss. A nominal baud rate is not the same as payload throughput: start, stop, parity, escaping, acknowledgments, and idle intervals consume capacity. Clock mismatch accumulates across an asynchronous character, which is why receiver sampling and agreed frame lengths constrain tolerance. In a multidrop bus, address collisions and termination are physical as well as software concerns.

Legacy serial conventions also persist in specialized roles. MIDI carries musical performance messages over a serial protocol, while JTAG uses serial scan paths to test and program digital hardware. Modern high-speed links may serialize wide internal data and recover the clock from transitions, reducing pin count but increasing equalization and signal-integrity demands. These examples show that “serial” describes an ordering strategy, not one universal connector, speed, or protocol.

Baud rate

The number of signal symbols transmitted per second; it equals bits per second only when each symbol represents one bit.

UART

A hardware interface that converts parallel data to and from an asynchronous serial bitstream.

Framing

The rules that mark data boundaries and identify fields such as payload, address, and error checks.

Differential signaling

Transmission using the voltage or current difference between conductors, improving resistance to common-mode noise.

CRC

A cyclic redundancy check, a compact calculation used to detect many accidental changes in a frame.