1. Protocol Introduction

DNP3 (Distributed Network Protocol) is commonly used in SCADA scenarios such as power and water utilities. It supports Integrity Scan and Event Scan, and can run over TCP/UDP/Serial.

NG Gateway DNP3 driver acts as Master communicating with Outstation:

• Periodically execute Integrity Scan (Class 0/1/2/3)
• Periodically execute Event Scan (Class 1/2/3)
• Support some downlink commands (CROB/Analog Output/Restart, etc.)

2. Configuration Model

2.1 Channel Configuration

2.1.1 connection.type (Connection Type)

• serial: Serial/RS-485 (Recommended for direct connection to 485 bus)
• tcp: TCP (Serial server/Gateway)
• udp: UDP (Serial server/Gateway)

Serial Parameters (When connection.type = serial):

• connection.port: Serial port path
• connection.baud_rate: Baud rate
• connection.data_bits: Data bits (Default 8)
• connection.stop_bits: Stop bits (Default 1)
• connection.parity: Parity

TCP Parameters (When connection.type = tcp):

• connection.host: Host
• connection.port: Port

UDP Parameters (When connection.type = udp):

• connection.host: Host
• connection.port: Port
• connection.localPort: Optional, local UDP port

2.1.2 Link Layer Address

• localAddr: Master address (0..65519)
• remoteAddr: Outstation address (0..65519)

2.1.3 Scan and Timeout

• responseTimeoutMs: Response timeout (Default 5000)
• integrityScanIntervalMs: Integrity scan interval (Default 20000)
• eventScanIntervalMs: Event scan interval (Default 1000)

2.2 Device Configuration

Driver layer device configuration is empty (device used for logical grouping).

2.3 Point Configuration

Points are located by "Object Group + Index":

• group: Object Group (BinaryInput/AnalogInput/Counter/OctetString etc.)
• index: Index (Starting from 0)

2.4 Action Configuration

Action is used to encapsulate a set of "Downlink Command" operations; Action itself does not carry protocol detail configuration.

• Key Semantics: DNP3 command type and target index should be configured on Action's inputs(Parameter), i.e., each parameter specifies the command and object index to issue via Parameter.driver_config.group/index.
• Parameterless Action: Commands like WarmRestart/ColdRestart usually do not need value; you can create an Action with empty inputs, and use Action.command to represent the action semantics (driver will ignore value).

Parameter-level driver configuration fields (Each input parameter):

• group: Command Type (CROB / AnalogOutputCommand / WarmRestart / ColdRestart)
• index: Target Index (Required for CROB/AnalogOutputCommand; Ignored for Restart class)

TIP

For details on group/index, see Object Group/Index/Command Type

3. Data Type Mapping Table

3.1 Point (Uplink) Recommended Mapping

Point group	Raw Value Type	Recommended DataType	Description
BinaryInput / BinaryOutputStatus (bool class)	bool	Boolean	Most recommended
AnalogInput (Analog)	f64	Float32 / Float64	Optional Int*/UInt* if integer needed, but watch for overflow and precision
Counter / FrozenCounter (Cumulative)	u64	UInt64 (Or Int64)	Cumulative usually unsigned; select Int64 only if negative value agreed by field
OctetString	bytes	Binary / String	String will try UTF-8, fallback to Binary on failure

Note

DNP3 has many object groups, for full list and modeling suggestions see Object Group/Index/Command Type. The table above gives the most common and stable combinations.

3.2 WritePoint (Downlink Write Point) DataType Selection

WritePoint only supports writing the following groups:

• BinaryOutput → Uses CROB (Control Relay Output Block)
• AnalogOutput → Uses AnalogOutputCommand (Group 41)

And the driver performs Strict Type Validation on value (Type mismatch directly rejected), so point.data_type must be selected correctly.

Write Target (point.group)	Underlying Command	Recommended DataType	Value Description
BinaryOutput	CROB	UInt8 (Recommended)	Only supports UInt8 Control Code: Value must be selected from gateway allowed value table (See crob.md)
AnalogOutput	AnalogOutputCommand	Int16 / Int32 / Float32 / Float64	DataType decides Group41 Variation (Var2/Var1/Var3/Var4)

DataType to Group41 Variation Mapping (Key)

Core Mechanism: DataType directly determines the Variation used by DNP3 write command:

DataType	DNP3 Variation	Protocol Meaning	Value Range
Int16 / UInt16	Group41Var2	16-bit Analog Output	-32768 ~ 32767
Int32 / UInt32	Group41Var1	32-bit Analog Output	-2^31 ~ 2^31-1
Float32	Group41Var3	Single-precision Float	IEEE 754 float
Float64	Group41Var4	Double-precision Float	IEEE 754 double

Why no need to configure Variation?

NG Gateway adopts Simplified Modeling strategy, this design simplifies configuration, users do not need to understand protocol details, while ensuring protocol compatibility. See DataType and Variation Mapping.

3.3 Action Parameter (Downlink Action Parameter) DataType Selection

Action Parameter follows same rules as WritePoint: Each parameter carries group/index, and parses value by its data_type.

• group=CROB: Recommend data_type=UInt8, value as CROB Control Code(u8) (Select from gateway allowed value table)

Note

Value type is u8, but driver only accepts 48 explicit combinations (Others will be rejected), see crob.md.

• group=AnalogOutputCommand: value only supports Int16/Int32/Float32/Float64 (Otherwise driver returns error)

3.3.1 How to configure "Protocol Level Fields" of CROB Parameter?

To ensure WritePoint is Simple and Safe, WritePoint path DOES NOT Provide control capability for CROB's count/on/off etc. "Protocol Level Fields":

• WritePoint (BinaryOutput): Only supports issuing value=ControlCode(u8), cannot control crobCount/crobOnTimeMs/crobOffTimeMs
• Action (CROB): Control crobCount/crobOnTimeMs/crobOffTimeMs via Parameter Level modeling fields (Thus different inputs within the same Action can configure different pulse timing and counts)