RS-232 V2 Connector – DB9

The MC-V2-DB9 is available in four configurations based on two variables: gender (male or female) and wiring (standard or null-modem). Selecting the correct combination requires knowing the gender of your device’s DB9 port and the wiring convention it uses for communication.

Male vs. Female — Matching the Port on Your Device

Gender on a DB9 connector refers to the physical pins or sockets on the connector end that plugs into your RS-232 device.

A male DB9 connector has nine protruding metal pins. It mates with a female DB9 port (a port with nine pin sockets) on your device. If you look at your device’s RS-232 port and see recessed holes arranged in two rows (the port that accepts a plug), you need a male connector.

A female DB9 connector has nine recessed sockets. It mates with a male DB9 port (a port with exposed pins) on your device. If you look at your device’s RS-232 port and see protruding pins, you need a female connector.

A simple field check: if your device’s port looks like it has pins sticking out, you need a female connector. If it has holes, you need a male connector.

Standard vs. Null-Modem — Matching the Wiring Convention

The wiring convention determines how the transmit (TX) and receive (RX) signal lines are routed inside the cable. Getting this wrong means data goes nowhere — or more accurately, the wrong device is talking and no one is listening.

Standard (Straight-Through) Wiring connects each pin number on one end to the same pin number on the other end. This works because DCE and DTE devices assign their TX and RX lines to opposite pin numbers by convention — so a straight-through DB9 cable automatically routes each side’s transmit line to the other’s receive line without any explicit crossing in the cable itself. Use this wiring when your RS-232 device is designated as DCE (common on instruments like scales, test equipment, and measurement devices with traditional serial ports) and the receiving end — in this case the RS-232 V2 Mobile Module — is designated as DTE.

Null-Modem Wiring crosses the TX and RX lines: the TX pin on one end connects to the RX pin on the other, and vice versa. This is required when both your RS-232 device and the interface are wired as DTE (Data Terminal Equipment), meaning both transmit on their TX pin. Without crossing those lines, both sides are transmitting on the same wire and listening on the same wire — and nothing gets through. The null-modem configuration resolves this by explicitly crossing TX and RX so that each side’s transmit line feeds the other’s receive line. Many modern RS-232 instruments — including gages and measurement devices — are wired as DTE, making null-modem wiring the more frequently required option.

Note: A full null-modem configuration also crosses the RTS/CTS and DTR/DSR handshaking lines. If your device requires hardware flow control, contact MicroRidge to confirm your wiring requirement before ordering.