DNP3 Serial Transport — RS-232 and RS-485 Configuration
Key Takeaway
How to configure DNP3 over serial RS-232 and RS-485 — baud rate, data link layer settings, radio modem integration, and multi-drop bus design.
Quick Answer
DNP3 over serial uses RS-232 (point-to-point) or RS-485 (multi-drop) physical layers. Configure baud rate (typically 9600-19200 for radio links), data link layer settings, and radio modem timing parameters. RS-485 is the most common transport for oilfield DNP3 SCADA using licensed radios.
Serial Port Settings
- Baud rate — Match master and all outstations. 9600 is common for radio; 19200-38400 for direct wire.
- Data bits — 8
- Parity — None (most common for DNP3)
- Stop bits — 1
Data Link Layer
The DNP3 data link layer adds framing, addressing, and CRC-16 error checking to each frame. Key settings: confirm mode (enable for unreliable links), frame timeout, and retry count.
Radio Modem Integration
DNP3 over radio requires careful timing configuration:
- RTS/CTS handshaking — Enable for keyed radios
- Key-up delay — Time for radio to key before transmitting (50-100ms typical)
- Turnaround delay — Time between receive and transmit for half-duplex radios
RS-485 Multi-Drop
Multiple outstations share an RS-485 bus with one master. Same RS-485 wiring practices apply — daisy-chain topology, 120-ohm termination at both ends, bias resistors at the master.
Frequently Asked Questions
9600 baud is most common for licensed narrowband radios. 19200 may be used on higher-bandwidth radios. The baud rate must match master, outstations, and radio configuration.
The serial port connects to the radio modem. RTS/CTS handshaking keys the radio before data transmission. Key-up delay and turnaround delay settings accommodate the radio's transmit/receive switching time.