LINEAR RS232 Quick User Guide

RS232 Quick Guide

TIA/EIA-232-F Standard

RS232 conveys data over a simple unterminated, multiconductor cable at rates up to 20k B. The RS232 standard specifies the electrical characteristics and connector for an all encompassing point-to-point modem interface. Although the original specification was intended for modems, subsequent renderings shed unneeded signals to expand its scope and use as a general purpose serial interface at data rates up to 1MB.

Specification RS232 Mode of Operation Single-Ended Number of Drivers and Receivers Allowed on One Line 1 Driver, 1 Receiver Maximum Cable Length 50 Feet* Maximum Data Rate 20k B/s Maximum Voltage Applied to Driver Output ±25V Driver Output Signal Minimum Loaded ±5V

Maximum Unloaded ±15V

Termination 3kΩ to 7kΩ Output Slew Rate 30V/µs (Max) Receiver Input Voltage Range ±25V Max Receiver Input Sensitivity ±3V Receiver Input Resistance 3kΩ to 7kΩ * For 2500p F cable capacitance, as per IEA 232D for data rates less than 20k baud. For data rates greater than 20k baud, CLOAD = 1000p F.

Signal Pinout Cable and Adapters DB25 DB9 Name ABBR. DTE ⇔ DCE Straight Through Minimum Straight

Cable Cable Null Modem Cable AT to 25-Pin Adapter

Frame Ground FG

DTE DCE DTE DCE DTE DCE 25-PIN 9-PIN

Transmit Data TD FG TD FG TD

Receive Data RD TD RD SG RD RD SG TD TD RTS

Request to Send RTS

RTS RTS RTS RD RD CTS

Clear to Send CTS

CTS CTS CTS RTS RTS DSR Data Set Ready DSR DSR DSR DSR CTS CTS SG SG DCD DCD DSR DTR DCD

Signal Ground SG

DTR DTRDCD DCD DTR

Data Carrier Detect DCD

TC (SYNC. ONLY) DTR DSR RI

(Reserved) RC (SYNC. ONLY) DCD

(Reserved) DTR

Unassigned

A minimum null modem cable is the same as a minimum straight cable except that RD and Sec. Carrier Detect (S) CD TD (Pins 2 and 3) are cross-connected as in the null modem cable.

Sec. Clear to Send (S) CTS

Connectors

Sec. Transmit Data (S) TD

DB25 DB9

Views are from the pin

Transmitter Clock TC

side of the female

Sec. Receive Data (S) RD (DCE) connector or

the wire side of the

Receiver Clock RC

male (DTE) connector.

Local Loopback Sec. Request to Send (S) RTS

Character Frame Relative Signal Timing

Data Terminal Ready DTR

Normal timing sequences during establishment of

Remote Loopback CHARACTER FRAME

communications are shown below. On half-duplex

DATA BIT

Signal Quality Detect SQ circuits, RTS is dropped as soon as the data is sent.

This is to signal a turnaround of the circuit.

Ring Indicator RI START STOP

BIT • • • MSB PAR BITLSB

Data Rate Select DTR

Transmitter Clock (E) TC DSR OTHER DATA BITS

OPTIONAL PARITY BIT

Test Mode RTS

MSB = MOST SIGNIFICANT DATA BIT

n The DTE ⇔ DCE column indicates data direction. CTS LSB = LEAST SIGNIFICANT DATA BIT n Pin numbers in bold indicate commonly used signals.

n Data rate select (Pin 23) can be from DTE or DCE.

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