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Short note: RS-232 standard

Short answer

RS-232 is a serial communication standard defining voltage levels (±3–15V), connectors (DB-9/DB-25), and signals like TxD, RxD, RTS, CTS. It connects DTE and DCE, requiring level converters (MAX232) for TTL compatibility, with limited speed and distance.

Write a short note on RS-232 standard.

RS-232 (RS-232C) is an EIA standard for serial data communication between a DTE (Data Terminal Equipment, e.g. a computer) and a DCE (Data Communication Equipment, e.g. a modem). It defines the electrical levels, connector, signals and handshaking.

Electrical specification

  • Logic 1 (mark): −3 V to −15 V; logic 0 (space): +3 V to +15 V; the range −3 V to +3 V is undefined. These are not TTL levels, so a converter such as the MAX232 (or 1488/1489) is used.
  • Maximum speed about 20 kbps (up to 115.2 kbps in practice) and maximum cable length about 15 m (50 ft).
  • Connector: 25-pin DB-25 or 9-pin DB-9.

Main signals (DB-9)

PinSignalMeaning
1DCDData carrier detect
2RxDReceived data
3TxDTransmitted data
4DTRData terminal ready
5GNDSignal ground
6DSRData set ready
7RTSRequest to send
8CTSClear to send
9RIRing indicator

Features: single-ended signalling (common ground), asynchronous or synchronous format, point-to-point link only. It is interfaced to the 8085/8086 through a USART such as the 8251A. Its limitations are low speed, short distance and sensitivity to noise, because the line is unbalanced.

✓ Answer checked by Claude Opus 5.5 (high effort)

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