RS232 Quick Guide
TIA/EIA-232-F Standard
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 Length50 Feet*Maximum Data Rate

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

Driver Output Signal

Minimum Loaded±5V

Maximum Unloaded±15VTermination

3kΩ to 7kΩ

Output Slew Rate

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

Receiver Input Sensitivity±3V

Receiver Input Resistance3kΩ to 7kΩ* 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
DB25

DB91

Cable and Adapters
Name
Frame GroundDTE ⇔ DCEStraight ThroughCableTD

⇒

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

ABBR.
FG

23Transmit Data

32Receive DataRD⇐

47Request to Send

RTS⇒

58Clear to Send

CTS⇐

66Data Set ReadyDSR⇐

75Signal GroundSG

81Data Carrier Detect

DCD⇐9(Reserved)

10(Reserved)

11

Unassigned

12Sec. Carrier Detect(S) CD⇐

13Sec. Clear to Send

(S) CTS⇐14Sec. Transmit Data

(S) TD⇒

15

Transmitter ClockTC⇐

16Sec. Receive Data

17

Receiver Clock18

Local Loopback

192042122(S) RD⇐RC⇐(S) RTS⇒

Data Terminal ReadyDTR⇒⇒

Remote Loopback
9Signal Quality Detect

SQ⇐Ring Indicator

RI⇐

Data Rate Select24

Transmitter Clock25

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

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

AT to 25-Pin Adapter
25-PIN
23456782022DCE
17TD
2RD
3RTS
4CTS5DTR20FG
SGDSR
6DCD
8TDRDRTSCTSDSR
SGDCD
DTRRI

9-PIN
327865149A 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.

Connectors
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.
DTRThe 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.
nDTE
2
3
7
RTS
4CTS
5DSR
6DCD
8DTR
20

54
93
8

2
7

16

⇒

Sec. Request to Send

23

Minimum Straight
Cable

⇒

DSR

⇐

RTS
CTS
TD

L, LT, LTC, LTM, Linear Technology and the Linear logo are registeredtrademarks of Linear Technology Corporation. All other trademarks are theproperty of their respective owners.

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

Character Frame
CHARACTER FRAMEDATA BITSTARTBITLSB• • •MSB

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

Linear Technology RS232 Transceivers
Number ofDrivers

Number ofReceivers

Supply(V)Data Rate(kbps)

ESD(kV)

11

3.3/5

1000

10

1
1222222222222222234444551122222222222222223045454

1.8 to 5
1.8 to 55555555555551.8 to 5
1.8 to 5
1.8 to 5
1.8 to 55555555250
1000
2502502502502502502501201201201201202502501000
1000
250250250250250250
250

10101010101010151522101010101010101521010101010LT1133A
LT1137A
LT1141A
LT1237
LT1330
LT1342
LT1537
LTC1337
LTC1347
LTC1348
LTC134933333333333555555555555555555553 to 5.55250250250250250250250120120120120151510151010210101010

Peripheral
LT1132A (DCE)
LT1135A
LT1138A
LT1140A
LTC13385555533333555552502502502501201010101010RS562
LTC1385
LTC1386
LT1331
LTC1327
LTC135022333225553.3
3.3
3 to 5
3.3
3.3120120250120
250

1010101010Part Number

DriverDisableShutdown
Mode

Temp.
Grade

•

C, I

LGA-32, BGA-32

•••

C, I
C, I
C, I
C, I
C, I
C, I
C, I
C, I
C, I
C, IC, I
C, I
C, I
C, I
C, I
C, I
C, I
C, I
C, I
C, I
C, IC
C
C, I
C

DFN-12
DFN-12SW-18, N-18
SW-16, N-16
SW-16, N-18
SW-16, N-16
SO-16
SW-18, N-18
SO-16, SW-16, N-16
SW-18, N-18
SO-16, N-16
SW-18, N-18
SO-16, N-16
SSOP-20, DIP-18, SO-18
DFN-16
SSOP-16
DFN-16
SSOP-16
SW-16, N-16
SW-14, N-14
SW-24, N-24
SW-28, N-28
SW-24, N-24
SW-28, N-28
SW-28, N-28••••••••C, I
C, ICC
C, ICCCCC, IC, I

SW-24, N-24
SSOP-28, SW-28, N-28
SW-24, N-24
SSOP-28, SW-28, N-28
SSOP-28, SW-28, N-28
SSOP-28, SW-28, N-28
SSOP-28, SW-28
SSOP-28, SW-28, N-28
SSOP-28, SW-28, N-28
SSOP-28, SW-28
SSOP-28, SW-28, N-28

•
••••
•

C, I
C
C, IC
C, I

SW-24, N-24
SW-20, N-20
SSOP-28, SW-28, N-28
SW-24, N-24
SSOP-28, SW-28, N-28

•

•••
•
•

C, I
C, IC
CC, I

SSOP-20, SO-18, DIP-18
SO-16
SSOP-28, SW-28, N-28
SSOP-28, SW-28, N-28SSOP-28, SW-28, N-28

Packages

2500VRMS Isolation
LTM2882-3/-5
General Purpose
LTC2801
LTC2802
LT1180A
LT1181A
LT1280A
LT1281A
LT1381
LT1780LT1781
LTC1080
LTC1081
LTC1382
LTC1383
LTC1384
LTC2803
LTC2803-1
LTC2804
LTC2804-1
LT1039A
LT1032
LT1134A
LT1136A
LT1139A
LT1130A
LT1131A

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PC Port (DTE)•

www.linear.com/RS232 n 1-800-4-LINEAR
1010B