RS232

9 PIN D-SUB MALE connector (computer side)

25 PIN D-SUB MALE connector
Pin DE9 | Pin DB25 | Signal | In/Out | Description |
1 | 8 | DCD | In | Data Carrier Detect |
2 | 3 | RXD | In | Receive Data |
3 | 2 | TXD | Out | Transmit Data |
4 | 20 | DTR | Out | Data Terminal Ready |
5 | 7 | GND | - | Ground |
6 | 6 | DSR | In | Data Set Ready |
7 | 4 | RTS | Out | Request To Send |
8 | 5 | CTS | In | Clear To Send |
9 | 22 | -RI | In | Ring Indicator |
Shell | | | Protective Ground |
(*) Pinout is at DTE (Computer) side
Null modem pin mapping:
Connector 1 | Connector 2 |
TxD | RxD |
RxD | TxD |
RTS | CTS |
CTS | RTS |
GND | GND |
DSR | DTR |
DCD |
DTR | DSR |
DCD |
RS232 on RJ45 (EIA-561)

8 pin RJ45 male connector (Plug)
RJ45 Pin N. | Name | DB9 Cross Connect | Description |
1 | DSR/RI | 6,9 | Data Set Ready/Ring Indicator |
2 | DCD | 1 | Data Carrier Detect |
3 | DTR | 4 | Data Terminal Ready |
4 | GND | 5 | Ground |
5 | RD | 2 | Receive Data |
6 | TD | 3 | Transmit Data |
7 | CTS | 8 | Clear to Send |
8 | RTS | 7 | Request to Send |