RS232 Connectors / Pinout
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The most common connectors for RS232 communications are
•9-pole SUB D9 (EIA/TIA 574 standard). Introduced by IBM and widely used. See below.
•25-pole SUB D25 (RS232-C). This is the original connector introduced for the RS232 standard. It provides a secondary communication channel.
•8-pole RJ45 (different pinouts for Cisco/Yost wiring, EIA/TIA-561, and other manufacturer-specific pinouts).
View: Looking into the male connector.
Pinout: From a DTE perspective (the DTE transmits data on the TX Transmit Data line, while the DCE receives data on this line)
Pin No. |
Signal Name |
Description |
DTE in/out |
1 |
DCD |
Data Carrier Detect |
Input |
2 |
RX |
Receive Data |
Input |
3 |
TX |
Transmit Data |
Output |
4 |
DTR |
Data Terminal Ready |
Output |
5 |
SGND |
Signal Ground |
- |
6 |
DSR |
Data Set Ready |
Input |
7 |
RTS |
Request To Send |
Output |
8 |
CTS |
Clear To Send |
Input |
9 |
RI |
Ring Indicator |
Input |
View: Looking into the male connector.
Pinout: From a DTE perspective.
Pin No. |
Signal Name |
Description |
1 |
- |
Protective/Shielding Ground |
2 |
TX |
Transmit Data |
3 |
RX |
Receive Data |
4 |
RTS |
Request To Send |
5 |
CTS |
Clear To Send |
6 |
DSR |
Data Set Ready |
7 |
SGND |
Signal Ground |
8 |
DCD |
Data Carrier Detect |
9 |
- |
Reserved |
10 |
- |
Reserved |
11 |
- |
Unassigned |
12 |
SDCD |
Secondary Data Carrier Detect |
13 |
SCTS |
Secondary Clear To Send |
14 |
STx |
Secondary Transmit Data |
15 |
TxCLK |
Transmit Clock |
16 |
SRx |
Secondary Receive Data |
17 |
RxCLK |
Receive Clock |
18 |
LL |
Local Loopback |
19 |
SRTS |
Secondary Request To Send |
20 |
DTR |
Data Terminal Ready |
21 |
RL/SQ |
Remote Loopback / Signal Qualify Detector |
22 |
RI |
Ring Indicator |
23 |
CH/CI |
Signal Rate Selector |
24 |
ACLK |
Auxiliary Clock |
25 |
- |
Unassigned |
Several conflicting pinouts exist and are in use for RJ45 connectors in RS232 communications:
Cisco Console / Yost Cable / Rollover cable applications
Pinout: From a DTE perspective (the DTE transmits data on the TX Transmit Data line)
Pin No. |
Signal Name |
Description |
1 |
CTS |
Clear To Send |
2 |
DCD |
Data Carrier Detect |
3 |
RX |
Receive Data |
4 |
SGND |
Signal Ground |
5 |
SGND |
Signal Ground |
6 |
TX |
Transmit Data |
7 |
DTR |
Data Terminal Ready |
8 |
RTS |
Request To Send |
NOTE: The Cisco/Yost pinout is used with cables that are wired "mirror image" on one end., similar to a Null Modem Cable with Handshaking. Every device has the same RJ45 female socket and transmits data on the same pin. See also the Yost Serial Device Wiring Standard .
EIA/TIA-561 standard for RJ45 / 8P8C modular connector
Pin No. |
Signal Name |
Description |
1 |
DSR / RI |
Data Set Ready / Ring Indicator |
2 |
DCD |
Data Carrier Detect |
3 |
DTR |
Data Terminal Ready |
4 |
SGND |
Signal Ground |
5 |
RX |
Receive Data |
6 |
TX |
Transmit Data |
7 |
CTS |
Clear To Send |
8 |
RTS |
Request To Send |
NOTE: Though this is an official standard, it is more likely that you will find RS232 RJ45 products with different pinout, either the Cisco/Yost variant above or manufacturer-specific pinouts, e.g. MOXA Nport.