RS485 pin diagram for wiring DB9 connector
RS485 is a standard defining the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. It is used extensively in industrial automation systems and other applications where reliable and robust communication over long distances and in electrically noisy environments is required.
Key Features
• RS485 uses differential signaling, which means it uses a pair of wires for each signal.
This allows for better noise immunity and longer communication distances.
• Multi-Point Configuration: It supports multiple devices (up to 32 nodes) on the same bus,
which makes it ideal for networked communications.
• Long Distance Communication: RS485 can communicate over distances up to 1200 meters (4000 feet) at lower speeds
(about 100 Kbps).
• High Speed: It can support data rates up to 10 Mbps, although speed decreases with longer cable lengths.
RS485 connector 9 pin diagram
Figure describes RS485 pin diagram for 9 pin connector. Tx+ and Tx- carry transmit data and Rx+ and Rx- carry receive data. Due to differential signals distance carried by signals are more.
As shown in the pin diagram, RS485 has all the signals in differential configurations.
RxD+ and RxD- used for receiving data
TxD+ and TxD- used for transmitting data
CTS+ and CTS- as well as
RTS+ and RTS- are used as handshake control signals
In a multi drop configuration about 32 devices can be connected with 1 master controlling device. One application of RS 485 interface is VSAT NMS (Network Management System), in which software application running on desktop PC is used to monitor and control many sub systems. These subsystems are Modems, MUXs, RF up converters, RF down converters and more. All the subsystems and PC housing NMS software should have RS485 connectors with cable wiring properly done to make this multi drop configuration work properly.
RS485 Technical Specifications
Following table-1 mentions technical specifications of RS 485 interface type.
| Specifications | RS485 |
|---|---|
| Mode of operation | Differential |
| number of drivers/receivers on one line | 1 driver, 32 receiver |
| maximum cable length | 4000 feet |
| maximum data rate | 30 Mbps |
| max. driver output voltage | -7V to +12V |
| Max. driver current in high impedance state (power off) | +/-100 µA |
| receiver input voltage range | -7V to +12V |
| Receiver input sensitivity | +/-200mV |
| Driver load impedance | 54 Ohms |
| Receiver Input Resistance | >=12 K Ohm |
Conclusion
The RS485 interface supports higher data rate and distance compare to RS232. The RS485 interface is a robust and versatile standard for serial communication, especially suited for industrial environments. Understanding the pinout of a typical 9-pin RS485 connector is essential for setting up and troubleshooting RS485 networks. Always ensure proper termination and biasing of the bus to maintain signal integrity. Also refer advantages and disadvantages of RS485 interface >>.