RS-232 (now TIA-232, formerly EIA-232) is a **1960s serial communication standard** for point - to - point links between Data Terminal Equipment (DTE, e.g., computers) and Data Communication Equipment (DCE, e.g., modems, peripherals).


Core Traits

Signaling & Mode:Uses single - ended signaling (logic 1: -3V to -25V; logic 0: +3V to +25V) — simpler wiring but prone to noise. Supports full - duplex (min 3 wires) and half - duplex (2 wires), with flow control via hardware (adds RTS/CTS, 5 wires for full - duplex) or software.
Data & Speed: Asynchronous serial transmission. Conventional frame: 1 start bit + 7/8 data bits + optional parity + 1/2 stop bits*. Baud rates: 1200–115200 bps (devices must match rates; high - speed support varies).


Interfaces & Connections

Connectors: Originally 25 - pin DB25, later simplified to 9 - pin DE9 (once standard on PCs); RJ - 45 is also used. DTE uses male connectors, DCE female.
Cabling: Straight - through cable for DTE - DCE; null modem (crossover) cable for same - device types (e.g., two computers). Max range: ~15m at 19200 bps (longer distances need low - capacitance cables/slower speeds, but other standards are better for that).


Use & Limits
 

Applications: Still used in industrial gear, instrumentation (e.g., meters, test tools) for short - range, low - speed links. Industrial PCs may have multiple RS - 232 ports (or expandability). No universal protocol — devices use unique command/data formats (so device - specific software or basic programming is needed).
Drawbacks vs New Tech: Slower, shorter - range, larger connectors, and no multipoint support vs RS - 485/Ethernet. USB has replaced it in most PC peripherals, but **USB - to - RS - 232 adapters** keep it usable.