LINEAR TECHNOLOGY RS232 Technical data
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.
LOAD
RS232
= 1000pF.
Specification
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/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 2500pF cable capacitance, as per IEA 232D for data rates less than 20k baud. For data rates greater than 20k baud, C
Signal Pinout
DB25 DB9 Name ABBR. DTE ⇔ DCE
1 Frame Ground FG
2 3 Transmit Data TD
3 2 Receive Data RD
4 7 Request to Send RTS
5 8 Clear to Send CTS
6 6 Data Set Ready DSR
7 5 Signal Ground SG
8 1 Data Carrier Detect DCD
9 (Reserved)
10 (Reserved)
11 Unassigned
12 Sec. Carrier Detect (S) CD
13 Sec. Clear to Send (S) CTS
14 Sec. Transmit Data (S) TD
15 Transmitter Clock TC
16 Sec. Receive Data (S) RD
17 Receiver Clock RC
18 Local Loopback
19 Sec. Request to Send (S) RTS
20 4 Data Terminal Ready DTR
21 Remote Loopback
Signal Quality Detect SQ
22 9 Ring Indicator RI
23 Data Rate Select
24 Transmitter Clock (E) TC
25 Test Mode
n
The DTE ⇔ DCE column indicates data direction.
n
Pin numbers in bold indicate commonly used signals.
n
Data rate select (Pin 23) can be from DTE or DCE.
Cable and Adapters
Straight Through
Cable
⇒
⇐
⇒
⇐
⇐
⇐
⇐
⇐
⇒
DTE
1
2
3
4
5
6
7
8
TC (SYNC. ONLY)
15
RC (SYNC. ONLY)
17
20
A minimum null modem cable is the same as a minimum straight cable except that RD and
TD (Pins 2 and 3) are cross-connected as in the null modem cable.
Connectors
FG
TD
RD
RTS
CTS
DSR
SG
DCD
DTR
DCE
⇐
⇐
⇐
13 12 11 10 9 8 7 6 5 4 3 2 1
25 24 23 22 21 20 19 18 17 16 15 14
⇒
⇒
⇒
⇒
⇐
⇐
⇒
⇐
Normal timing sequences during establishment of
communications 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
DSR
RTS
CTS
TD
Minimum Straight
Cable
DTE
TD
2
1
2
3
4
5
6
7
8
15
17
20
DB25 DB9
RD
3
SG
7
RTS
4
CTS
5
DSR
6
DCD
8
DTR
20
RTS
CTS
DSR
DCD
DTR
DCE
2
3
7
4
5
6
8
20
Null Modem Cable
DTE
1
7
TD
2
RD
3
RTS
4
CTS
5
DSR
6
DCD
8
DTR
20
5 4 3 2 1
9 8 7 6
Character FrameRelative Signal Timing
START
BIT
OTHER DATA BITS
MSB = MOST SIGNIFICANT DATA BIT
LSB = LEAST SIGNIFICANT DATA BIT
DCE
FG
SG
1
7
TD
2
RD
3
RTS
4
CTS
5
DTR
20
DSR
6
DCD
8
Views are from the pin
side of the female
(DCE) connector or
the wire side of the
male (DTE) connector.
CHARACTER FRAME
DATA BIT
• • • MSB
LSB
OPTIONAL PARITY BIT
AT to 25-Pin Adapter
25-PIN
TD
2
RD
3
RTS
4
CTS
5
DSR
6
SG
7
DCD
8
DTR
20
RI
22
STOP
PAR
9-PIN
3
2
7
8
6
5
1
4
9
BIT
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Linear Technology RS232 Transceivers
Part Number
2500V
General Purpose
PC Port (DTE)
Isolation
RMS
LTM2882-3/-5 1 1 3.3/5 1000 10 • C, I LGA-32, BGA-32
LTC2801 1 1 1.8 to 5 250 10 • • C, I DFN-12
LTC2802 1 1 1.8 to 5 1000 10 • • C, I DFN-12
LT1180A 2 2 5 250 10 • C, I SW-18, N-18
LT1181A 2 2 5 250 10 C, I SW-16, N-16
LT1280A 2 2 5 250 10 • C, I SW-16, N-18
LT1281A 2 2 5 250 10 C, I SW-16, N-16
LT1381 2 2 5 250 10 C, I SO-16
LT1780 2 2 5 250 15 • C, I SW-18, N-18
LT1781 2 2 5 250 15 C, I SO-16, SW-16, N-16
LTC1080 2 2 5 120 2 • C, I SW-18, N-18
LTC1081 2 2 5 120 2 C, I SO-16, N-16
LTC1382 2 2 5 120 10 • C, I SW-18, N-18
LTC1383 2 2 5 120 10 C, I SO-16, N-16
LTC1384 2 2 5 120 10 • C, I SSOP-20, DIP-18, SO-18
LTC2803 2 2 1.8 to 5 250 10 • • C, I DFN-16
LTC2803-1 2 2 1.8 to 5 250 10 • • C, I SSOP-16
LTC2804 2 2 1.8 to 5 1000 10 • • C, I DFN-16
LTC2804-1 2 2 1.8 to 5 1000 10 • • C, I SSOP-16
LT1039A 3 3 5 250 15 • C, I SW-16, N-16
LT1032 4 0 5 250 2 • C, I SW-14, N-14
LT1134A 4 4 5 250 10 C, I SW-24, N-24
LT1136A 4 5 5 250 10 • C SW-28, N-28
LT1139A 4 4 5 250 10 • C SW-24, N-24
LT1130A 5 5 5 250 10 C, I SW-28, N-28
LT1131A 5 4 5 250 10 • • C SW-28, N-28
LT1133A 3 5 5 250 15 C, I SW-24, N-24
LT1137A 3 5 5 250 15 • • C, I SSOP-28, SW-28, N-28
LT1141A 3 5 5 250 10 • C SW-24, N-24
LT1237 3 5 5 250 15 • • C SSOP-28, SW-28, N-28
LT1330 3 5 5 250 10 • • C, I SSOP-28, SW-28, N-28
LT1342 3 5 5 250 10 • C SSOP-28, SW-28, N-28
LT1537 3 5 5 250 2 • • C SSOP-28, SW-28
LTC1337 3 5 5 120 10 • C SSOP-28, SW-28, N-28
LTC1347 3 5 5 120 10 • C SSOP-28, SW-28, N-28
LTC1348 3 5 3 to 5.5 120 10 • C, I SSOP-28, SW-28
LTC1349 3 5 5 120 10 • C, I SSOP-28, SW-28, N-28
Drivers
Number of
Number of
Receivers
Supply
(V)
Data Rate
(kbps)
ESD
(kV)
Driver
Disable
Shutdown
Mode
Temp.
Grade Packages
Peripheral (DCE)
LT1132A 5 3 5 250 10 C, I SW-24, N-24
LT1135A 5 3 5 250 10 C SW-20, N-20
LT1138A 5 3 5 250 10 • • C, I SSOP-28, SW-28, N-28
LT1140A 5 3 5 250 10 • • C SW-24, N-24
LTC1338 5 3 5 120 10 • • C, I SSOP-28, SW-28, N-28
RS562
LTC1385 2 2 3.3 120 10 • • C, I SSOP-20, SO-18, DIP-18
LTC1386 2 2 3.3 120 10 C, I SO-16
LT1331 3 5 3 to 5 250 10 • • C SSOP-28, SW-28, N-28
LTC1327 3 5 3.3 120 10 • C SSOP-28, SW-28, N-28
LTC1350 3 5 3.3 250 10 • C, I SSOP-28, SW-28, N-28
www.linear.com/RS232 n 1-800-4-LINEAR
1010B
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