RS232 Null Modem Cable Pinout (DB9-DB9)
In modern software development, physical cables are often replaced by Virtual Null Modem (also known as a Virtual COM Port driver) to facilitate testing on a single local computer. A virtual null modem creates a pair of interlinked virtual COM ports (e.g., COM3 and COM4) in the operating system; any data sent to one port is instantly received by the other. This allows developers to test communication between two different applications. For example, you can connect a data logger and a terminal emulator on the same machine without physical serial hardware (usefult on modern laptops without ports).
Use this cable between two DTE (Data Terminal Equipment) devices (for instance two computers).
 | DB9 pin D-SUB female to PC1 |
| DB9 pin D-SUB female to PC2 |
| DB9-1 | DB9-2 | ||
|---|---|---|---|
| Receive Data | 2 | 3 | Transmit Data |
| Transmit Data | 3 | 2 | Receive Data |
| Data Terminal Ready | 4 | 6+1 | Data Set Ready + Carrier Detect |
| System Ground | 5 | 5 | System Ground |
| Data Set Ready + Carrier Detect | 6+1 | 4 | Data Terminal Ready |
| Request to Send | 7 | 8 | Clear to Send |
| Clear to Send | 8 | 7 | Request to Send |
Null modem (crossed) cable DB9-25 pin
Null modem (crossed) cable DB25-25 pin
Modem (straight) cable (DB9-DB25)
Modem (straight) cable (DB25-DB25)
Modem (straight) cable (DB9-DB15)