3-wire RS232 explained: TX, RX, and ground
Many RS232 devices communicate with only three electrical connections: transmit, receive, and ground. That simple arrangement is often called 3-wire RS232.
The three signals
- TX: data transmitted out of one device.
- RX: data received by that device.
- GND: the signal reference shared by the two endpoints.
For communication to work, the transmitter on one side must ultimately reach the receiver on the other side, and both sides need the correct signal reference.
Why TX and RX can be confusing
Pin labels are normally written from the perspective of the device being documented. A pin marked TX is the pin that device transmits on. A pin marked RX is the pin that device receives on.
This is why two pieces of equipment may need a crossover or null-modem arrangement: one endpoint's transmit signal must arrive at the other endpoint's receive input.
What 3-wire RS232 leaves out
The classic DB9 RS232 connector can carry more than just TX, RX, and ground. Other pins may be used for signals such as RTS, CTS, DTR, DSR, DCD, or RI.
Those extra lines can provide hardware flow control, modem status, connection-state information, or application-specific behavior. If the equipment requires one of them, a three-wire bridge cannot reproduce that behavior just by changing software.
When 3-wire RS232 is enough
A three-wire connection is a strong fit when the application handles data flow entirely through the serial byte stream and does not rely on external modem-control lines.
Common examples include devices that use ordinary request/response commands, periodic data output, or software-level acknowledgements. The important point is not the industry or device type; it is the actual serial-interface requirements.
Serial settings still have to match
Three correct wires are only part of the connection. Both endpoints also need compatible communication settings, including:
- baud rate,
- data bits,
- parity,
- stop bits,
- and any timing or packetization assumptions made by the application.
A familiar shorthand such as 9600 8N1 means 9600 baud, 8 data bits, no parity, and 1 stop bit.
DB9 does not automatically mean standard 3-wire RS232
A DB9 connector is only a physical connector. Equipment manufacturers have used DB9 connectors for RS232, RS485, CAN, TTL-level serial, proprietary signals, and custom pinouts.
GhostBridge GB-01 as a 3-wire RS232 bridge
The current production GhostBridge GB-01 uses a DB9 male connector with:
- Pin 2: RX into GhostBridge.
- Pin 3: TX out of GhostBridge.
- Pin 5: signal ground.
RTS/CTS and the other modem-control signals are not routed on the current GB-01 hardware. That makes it appropriate to describe the product specifically as a standard 3-wire RS232 bridge rather than a universal full-handshake DB9 device server.
How to evaluate your device
Before connecting a wireless serial bridge, find the device manual and answer four questions: Is it true RS232? Which pins are TX, RX, and ground? What serial settings are required? Does the device require any additional control lines?
If those answers point to ordinary three-wire communication, the device is a much stronger candidate for a bridge such as GhostBridge.
See the RS232 over WiFi guide for the complete network-side picture.