The RS 232 Standard is a serial connection that supports both asynchronous and synchronous connections. The RS-232 Standard has gone through several revisions. The DB25 connector is defined by RS-232C, the most common (on PCs, etc.) DE9 connector is defined by EIA/TIA 574 (a less common DE9 pintout was defined by EIA/TIA 232 and was used on older MicroVAX systems, some printers, etc.), and the RJ45 connector is defined by RS-232D.
DB 25 RS-232C Pinout |
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Pin |
Signal |
Abbreviation |
DTE |
DCE |
1 |
Shield/Frame (Earth) Ground |
GND |
- |
- |
2 |
Transmit Data |
TxD |
Out |
In |
3 |
Receive Data |
RxD |
In |
Out |
4 |
Request to Send |
RTS |
Out |
In |
5 |
Clear to Send |
CTS |
In |
Out |
6 |
Data Set Ready |
DSR |
In |
Out |
7 |
Signal Ground |
SGND |
- |
- |
8 |
Data Carrier Detect |
DCD |
In |
Out |
9 |
Test Voltage +Vdc |
+V |
In |
Out |
10 |
Test Voltage -Vdc |
-V |
In |
Out |
11 |
Unassigned |
- |
- |
- |
12 |
Secondary DCD |
SDCD |
In |
Out |
13 |
Secondary CTS |
SCTS |
In |
Out |
14 |
Secondary TxD |
STxD |
Out |
In |
15 |
Transmitted Signal Element Timing |
- |
In |
Out |
16 |
Secondary RxD |
SRxD |
In |
Out |
17 |
Received Signal Element Timing |
- |
In |
Out |
18 |
Local Loopback |
LL |
Out |
In |
19 |
Secondary RTS |
SRTS |
Out |
In |
20 |
Data Terminal Ready |
DTR |
Out |
In |
21 |
Remote LL / Signal Quality Detection |
RL/SQ |
Out/In |
In/Out |
22 |
Ring Indicator |
RI |
In |
Out |
23 |
Data Signal Rate Selector |
CH/CI |
Out/In |
In/Out |
24 |
Transmit Signal Element Timing |
- |
Out |
In |
25 |
Test Mode |
- |
In |
Out |
DE9 EIA/TIA 574 Pinout |
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Pin |
Signal |
Abbreviation |
DTE |
DCE |
1 |
Data Carrier Detect |
DCD |
In |
Out |
2 |
Received Data |
RxD |
In |
Out |
3 |
Transmitted Data |
TxD |
Out |
In |
4 |
Data Terminal Ready |
DTR |
Out |
In |
5 |
Signal Ground |
SGND |
- |
- |
6 |
Data Set Ready |
DSR |
In |
Out |
7 |
Request to Send |
RTS |
Out |
In |
8 |
Clear to Send |
CTS |
In |
Out |
9 |
Ring Indicator |
RI |
In |
Out |
DE9 EIA/TIA 232 Pinout |
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Pin |
Signal |
Abbreviation |
DTE |
DCE |
1 |
Shield/Frame (Earth) Ground |
GND |
- |
- |
2 |
Transmitted Data |
TxD |
Out |
In |
3 |
Received Data |
RxD |
In |
Out |
4 |
Request To Send |
RTS |
Out |
In |
5 |
Data Terminal Ready |
DTR |
Out |
In |
6 |
Data Set Ready |
DSR |
In |
Out |
7 |
Signal Ground |
SGND |
- |
- |
8 |
Clear to Send (?) |
CTS(?) |
In |
Out |
9 |
Data Carrier Detect (?) |
DCD(?) |
In |
Out |
RS-232D RJ 45 Pinout |
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Pin |
Signal |
Abbreviation |
DTE |
DCE |
1 |
DCE Ready, Ring Indicator |
DSR/RI |
In |
Out |
2 |
Data Carrier Detect |
DCD |
In |
Out |
3 |
DTE Ready |
DTR |
Out |
In |
4 |
Signal Ground |
SGND |
- |
- |
5 |
Received Data |
RxD |
In |
Out |
6 |
Transmitted Data |
TxD |
Out |
In |
7 |
Clear to Send |
CTS |
In |
Out |
8 |
Request to Send |
RTS |
Out |
In |