DB9 Female to female Mini Null Modem Adapter gender changer serial port cable connector.
 
A DB9 Female to Female connector (also known as a DB9 Gender Changer or coupler) is used to connect two male DB9 cables together or to convert a male port into a female port for RS-232 serial communication. When buying or using one, it is critical to match the internal wiring to your specific equipment needs.
 
Internal Wiring Configurations
Straight-Through Coupler:
Pins connect directly 1->1, 2 -> 2, 3 -> 3, up to 9 -> 9. Best for extending existing standard serial cables.
Null Modem Coupler:
Pins cross over internal transmit and receive lines (typically pins 2 and 3 cross, alongside ground on pin 5).
Best for establishing direct data communication between two computers or DTE devices.