RS232 DB25 Pinout and Signals: 25-pin Connector, Male and Female
This page lists all 25 pins of the RS232 (EIA-232) port on a DB-25 connector, with the direction of every signal between the computer (DTE) and a modem (DCE). Most PCs expose only nine of these signals on a 9-pin connector: see the DB9 pinout. The RS232 pinout of the other connectors (DB9, DB15, DB25 and RJ45) is collected on one page, and the meaning of each line, including RTS/CTS and DTR/DSR flow control, is explained under RS232 signals and hardware handshaking.
Fig. 1. DB25 male connector (computer side), front view
Fig. 2. DB25 female connector (modem or cable side), front view
Which side is which: the computer (DTE) has a male connector, so the cable end that plugs into it is female; a modem (DCE) has a female socket and takes a male cable end. Looking at the face of a male connector, pin 1 is at the top left; a female connector is the mirror image, with pin 1 at the top right. Both diagrams show the front view, and most connectors have the pin numbers moulded next to the holes.
 | DB25 pin D-SUB male at the DTE (Computer) |
 | DB25 pin D-SUB female at the DCE (Modem) |
| Pin | Name | Direction | Description |
|---|---|---|---|
| 1 | GND | Shield Ground | |
| 2 | TXD | → | Transmit Data |
| 3 | RXD | ← | Receive Data |
| 4 | RTS | → | Request to Send |
| 5 | CTS | ← | Clear to Send |
| 6 | DSR | ← | Data Set Ready |
| 7 | GND | System Ground | |
| 8 | CD | ← | Carrier Detect |
| 9 | - | - | RESERVED |
| 10 | - | - | RESERVED |
| 11 | STF | → | Select Transmit Channel |
| 12 | S.CD | ← | Secondary Carrier Detect |
| 13 | S.CTS | ← | Secondary Clear to Send |
| 14 | S.TXD | → | Secondary Transmit Data |
| 15 | TCK | ← | Transmission Signal Element Timing |
| 16 | S.RXD | ← | Secondary Receive Data |
| 17 | RCK | ← | Receiver Signal Element Timing |
| 18 | LL | → | Local Loop Control |
| 19 | S.RTS | → | Secondary Request to Send |
| 20 | DTR | → | Data Terminal Ready |
| 21 | RL | → | Remote Loop Control |
| 22 | RI | ← | Ring Indicator |
| 23 | DSRS | → | Data Signal Rate Selector |
| 24 | XCK | → | Transmit Signal Element Timing |
| 25 | TI | ← | Test Indicator |
Note: Do not connect SHIELD(1) to GND(7).
RS232 port related links
- DB9 pinout of the 9-pin PC serial port and the DB25 pinout as wired on PC COM ports.
- RS232 connectors: DB9, DB15, DB25 and RJ45 pinouts on one page.
- RS232 signals and hardware flow control (RTS/CTS, DTR/DSR); DTE and DCE explained.
- RS232 null modem cable pinout (DB9-DB9) and null modem cable (DB9-DB25) to connect two computers.
- Modem cable (DB9-DB25) and modem cable (DB9-DB15) for DTE to DCE connections.
- Serial data transfer cable with and without handshaking.
- Serial printer connector pinout and the serial printer cable (DB9-DB25).
- RS232 loopback plug (DB9 and DB25) to test a port.
- RS232 RJ45 pinout: EIA-561 and Cisco console wiring.
- DB15 serial pinout: X.21 and 15-pin RS232 cables.
- Serial port interface serial port interface description.
- List of serial ports in Windows: which COM ports your PC has and which program uses them.
- RS232 software: terminal, sniffer, data logger and RS232 to TCP bridge for Windows.