RS-422 DB9 Industrial Serial Connector
9-pin d-sub connector
Standards: TIA/EIA-422, ITU-T V.11, ISO 8482
What is the RS-422 DB9 pinout?
The RS-422 DB9 Industrial Serial Connector has 9 pins. Pin 1 is TX- (data). Pin 2 is TX+ (data). Pin 3 is RX+ (data). Pin 4 is RX- (data). Plus 5 more pins.
Standards: TIA/EIA-422, ITU-T V.11, ISO 8482
Pin Assignment Table
| Pin | Signal | Type | Description |
|---|---|---|---|
| 1 | TX- | data | Transmit Data - (TXD-) |
| 2 | TX+ | data | Transmit Data + (TXD+) |
| 3 | RX+ | data | Receive Data + (RXD+) |
| 4 | RX- | data | Receive Data - (RXD-) |
| 5 | GND | ground | Signal Ground |
| 6 | RTS- | data | Request To Send - (optional) |
| 7 | RTS+ | data | Request To Send + (optional) |
| 8 | CTS+ | data | Clear To Send + (optional) |
| 9 | CTS- | data | Clear To Send - (optional) |
Signal Types
Common Applications
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Map this connector into your BOM workflow →The RS-422 DB9 connector has 9 pins: Pin 1 (TX-), Pin 2 (TX+), Pin 3 (RX+), and Pin 4 (RX-). Plus 5 more pins. Common in Industrial automation and PLC communication.
RS-422 DB9 Pinout & Wiring Guide
RS-422 (TIA/EIA-422) is a balanced differential serial standard designed for industrial environments where electrical noise, long cable runs, or high data rates make single-ended RS-232 unreliable. Using differential signaling with voltage levels of +/- 2V to +/- 6V across twisted pairs, RS-422 achieves excellent common-mode noise rejection up to +/- 7V. The standard supports data rates from DC to 10 Mbps with cable lengths inversely proportional to speed - up to 1200m at 100 kbps or 10m at 10 Mbps. RS-422 is a one-driver, multi-receiver standard (up to 10 receivers per driver), making it ideal for broadcast or monitoring applications in factory automation.
Wiring Tips & Best Practices
RS-422 requires two twisted pairs for full-duplex communication: TX+/TX- (transmit differential pair) and RX+/RX- (receive differential pair). Always use shielded twisted pair (STP) cable with 100-120 ohm characteristic impedance. Connect shield to ground at one end only (typically the host/master side) to prevent ground loops. Terminate the line with a 100-120 ohm resistor across the differential pair at the far end of the cable to prevent reflections. For multi-drop configurations, only the last receiver on the bus should have termination. Pin assignments vary by manufacturer - always verify with equipment documentation. Common convention: TX+ on higher pin number than TX-.
Common Issues
Swapped TX+/TX- or RX+/RX- polarity causes inverted data or no communication - swap the pair if data appears corrupted. Missing or incorrect termination resistors cause signal reflections resulting in bit errors at higher speeds or longer distances. Ground loops from shield connected at both ends create noise and intermittent errors. Mixing RS-422 with RS-485 equipment can work but RS-422 drivers may not meet RS-485 load requirements. Cable capacitance limits maximum speed/distance - use low-capacitance cable for long runs. Some equipment labels pins as A/B instead of +/- with inconsistent conventions - verify with an oscilloscope or documentation.
Why Use Interactive Diagrams?
- Accuracy: Hover over pins to see exact signal names and descriptions
- Clarity: Color-coded by signal type (power, ground, data)
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