RS232 Quick Guide
TIA/EIA-232-F Standard
TIA/Ed
RS232 conveys data over a simple unterminated, multiconductor cable at rates up to 20kB. 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

20kB/sMaximum Voltage Applied to Driver Output±25V

Driver Output Signal

Minimum Loaded±5V

Maximum Unloaded±15V

Termination

3k< to 7k<

Output Slew Rate

30V/µs (Max)Receiver Input Voltage Range±25V Max

Receiver Input Sensitivity±3V

Receiver Input Resistance3k< to 7k<* For 2500pF cable capacitance, as per IEA 232D for data rates less than 20k baud. For data rates greater than 20k baud, CLOAD = 1000pF.

Signal Pinout
DB25DB91Cable and Adapters
Name
Frame Ground

ABBR.

DTE DCE

Straight Through
Cable
DTE
DCEFG
11TD
22RD
33RTS
44CTS
55DSR
66SG
77DCD
88TC (SYNC. ONLY)
1515RC (SYNC. ONLY)
1717DTR
2020FG

23Transmit DataTD¡

32Receive Data

RD



47

Request to Send

RTS¡

58Clear to Send

CTS



66

Data Set ReadyDSR

75Signal Ground

SG81

Data Carrier DetectDCD

9(Reserved)

10(Reserved)

11

Unassigned

12Sec. Carrier Detect(S) CD

13Sec. Clear to Send

(S) CTS

14Sec. Transmit Data(S) TD¡

15

Transmitter Clock

TC



16

Sec. Receive Data(S) RD

17

Receiver Clock

RC

18

Local Loopback

1920421
22

Sec. Request to Send(S) RTS¡DTR¡¡

Remote Loopback
9Signal Quality Detect

SQ

Ring Indicator

RI

Data Rate Select24

Transmitter Clock25

Test ModeDTE
237RTS
4CTS
5DSR
6DCD
8DTR
20TD
RD
SGDCE
237RTS
4CTS
5DSR
6
DCD
8DTR
20

Null Modem Cable
DTE
17TD
2RD
3RTS
4CTS
5DSR
6DCD
8DTR
20

AT to 25-Pin Adapter

DCE
17TD
2RD3RTS4CTS
5DTR20FG
SGDSR6DCD
8Connectors
13 12 11 10 9DB25876DB95432125 24 23 22 21 20 19 18 17 16 15 14

Relative Signal Timing
Normal timing sequences during establishment ofcommunications are shown below. On half-duplex
circuits, RTS is dropped as soon as the data is sent.
This is to signal a turnaround of the circuit.
DTR(E) TC

The DTE DCE column indicates data direction.
Pin numbers in bold indicate commonly used signals.
n Data rate select (Pin 23) can be from DTE or DCE.

25-PIN23456782022TDRDRTSCTSDSR
SGDCD
DTR
RI9-PIN
327865
149A minimum null modem cable is the same as a minimum straight cable except that RD andTD (Pins 2 and 3) are cross-connected as in the null modem cable.

5493
82
7Views are from the pinside of the female(DCE) connector or
the wire side of themale (DTE) connector.

16¡

Data Terminal Ready

23

Minimum Straight
Cable

¡

DSR

RTSnCTSn

TD

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Character Frame
CHARACTER FRAMEDATA BITSTARTBITLSBMSB

OTHER DATA BITS
OPTIONAL PARITY BITMSB = MOST SIGNIFICANT DATA BIT
LSB = LEAST SIGNIFICANT DATA BITPARSTOPBIT