DB9 Pinout Diagram for RS-232 Serial Wiring
9-pin d-sub connector
Standards: RS-232, EIA/TIA-232, ITU-T V.24
What is the DB9 pinout?
The DB9 Serial Connector (RS-232) has 9 pins. Pin 1 is DCD (data). Pin 2 is RXD (data). Pin 3 is TXD (data). Pin 4 is DTR (data). Plus 5 more pins.
Standards: RS-232, EIA/TIA-232, ITU-T V.24
Pin Assignment Table
| Pin | Signal | Type | Description |
|---|---|---|---|
| 1 | DCD | data | Data Carrier Detect |
| 2 | RXD | data | Receive Data |
| 3 | TXD | data | Transmit Data |
| 4 | DTR | data | Data Terminal Ready |
| 5 | GND | ground | Signal Ground |
| 6 | DSR | data | Data Set Ready |
| 7 | RTS | data | Request To Send |
| 8 | CTS | data | Clear To Send |
| 9 | RI | data | Ring Indicator |
Signal Types
Common Applications
Need another printable connector reference?
Use the pinout as a working reference now, then jump to the full library or the next workflow when you need it.
Browse the full pinout library →The DB9 connector has 9 pins: Pin 1 (DCD), Pin 2 (RXD), Pin 3 (TXD), and Pin 4 (DTR). Plus 5 more pins. Common in Serial communication and Industrial control.
DB9 RS-232 Pinout Reference
The DE-9 (often called DB9) connector is the standard interface for RS-232 serial communication. Unlike modern USB, RS-232 is a point-to-point protocol that requires specific crossover (Null Modem) wiring for connecting two DTE devices.
Wiring Tips & Best Practices
A common source of frustration is the distinction between DTE (Data Terminal Equipment, e.g., PC) and DCE (Data Circuit-terminating Equipment, e.g., Modem). A straight-through cable connects DTE to DCE. A Null Modem cable connects DTE to DTE.
Common Issues
Voltage levels: True RS-232 operates at +/- 12V, which can damage 5V (TTL) or 3.3V devices if connected directly without a level shifter (like a MAX232).
Why Use Interactive Diagrams?
- Accuracy: Hover over pins to see exact signal names and descriptions
- Clarity: Color-coded by signal type (power, ground, data)
- Printable: Export clean diagrams for shop floor reference