1) Point: Object Group (group) and Index

DNP3 data points usually consist of several key points:

• Object Group
• Variation
• Index

NG Gateway current version simplifies to:

• group: Object Group (Enum)
• index: Index

Common group meanings:

• BinaryInput: Digital Input
• DoubleBitBinaryInput: Double Bit Digital Input
• BinaryOutput: Digital Output Status
• Counter: Counter
• FrozenCounter: Frozen Counter
• AnalogInput: Analog Input
• AnalogOutput: Analog Output Status
• OctetString: Octet String

Modeling Suggestion:

• BinaryInput / DoubleBitBinaryInput: Recommend data_type=Boolean or UInt8 (Per field semantics)
• AnalogInput: Recommend Float32/Float64 (Configure scale if necessary)
• Counter / FrozenCounter: Recommend UInt32/UInt64
• OctetString: Recommend String or Binary

2) DataType and DNP3 Variation Mapping Relationship

2.1 Design Philosophy

In DNP3 protocol, each Object Group has multiple Variations, for example:

Group	Variation	Meaning
30	1	32-bit Analog Input With Flag
30	2	16-bit Analog Input With Flag
30	3	32-bit Analog Input Without Flag
30	5	Single-precision (Float32) With Flag
30	6	Double-precision (Float64) With Flag

NG Gateway adopts Simplified Modeling strategy:

• Read Direction: Use Class Data request, let Outstation decide which Variation to return
• Write Direction: Implicitly select corresponding Variation via DataType field

Advantages of this design:

1. Best Compatibility: Different Outstations may support different Variations
2. User Friendly: No need to deeply understand DNP3 protocol details
3. Compliant with IEEE 1815 Standard: Class Data is the recommended data request method

2.2 Variation Handling on Read

When NG Gateway executes Integrity Scan or Event Scan:

Master (NG Gateway)                    Outstation
        |                                   |
        |--- READ Class 0/1/2/3 ----------->|
        |    (Group60Var1~4)                |
        |                                   |
        |<-- Response with actual data -----|
        |    (Group30Var1 or Var5 etc.)     |

• Driver underlying library (dnp3-rs) will unify convert responses of different Variations to standard Rust types
• For example: Group30Var1, Group30Var5, Group30Var6 are all converted to AnalogInput { value: f64, flags: Flags, time: Option<Time> }
• Your configured DataType is used for Final Value Conversion (e.g., f64 → Int32 truncation)

Important

In uplink path, your DataType configuration does not affect request, only affects type conversion of the final value.

2.3 Variation Selection on Write

When writing commands (WritePoint / Action), DataType directly determines which DNP3 Variation to use:

Analog Output Command (AnalogOutputCommand - Group 41)

DataType	DNP3 Variation	Description
Int16 / UInt16	Group41Var2	16-bit Analog Output
Int32 / UInt32	Group41Var1	32-bit Analog Output
Float32	Group41Var3	Single-precision Float
Float64	Group41Var4	Double-precision Float

CROB Command (Control Relay Output Block - Group 12)

CROB always uses Group12Var1:

DataType	Value Parsing	Description
UInt8 (Recommended)	value=u8 (Control Code)	Product-level unified semantics: Downlink value only accepts numeric control code; but gateway only allows explicit safe subset (See crob.md)

2.3.1 CROB Control Code Bitfield Semantics

In NG Gateway current implementation, CROB ControlCode is an 8-bit bitfield, composed of:

• bits 7..6: Trip/Close Code (TCC)
  • 0b00 → Nul
  • 0b01 → Close
  • 0b10 → Trip
  • 0b11 → Reserved (Gateway Rejects)
• bit 5: clear
• bit 4: queue (Obsolete in standard, but still representable; support depends on Outstation)
• bits 3..0: OpType (Operation Type)
  • 1 → PulseOn
  • 2 → PulseOff
  • 3 → LatchOn
  • 4 → LatchOff
  • 0/5..15 (Gateway Rejects)

Common Control Code Examples

Note

Table below assumes tcc=Nul, clear=false, queue=false, so control code is op (low 4 bits). Note gateway Disallows op=0(Nul).

If you need Trip/Close or queue/clear, please refer to gateway allowed values, full value table see crob.md.

Semantics	op_type	control_code (Dec)	control_code (Hex)
PulseOn	PulseOn	1	0x01
PulseOff	PulseOff	2	0x02
LatchOn	LatchOn	3	0x03
LatchOff	LatchOff	4	0x04

2.4 Full Variation Reference Table

Below are main Variations of DNP3 object groups and their usage (For reference):

Binary Input (Group 1/2)

Group	Var	Type	Description
1	1	Static	Packed Format (No flags)
1	2	Static	With Flags
2	1	Event	Without Time
2	2	Event	With Absolute Time
2	3	Event	With Relative Time

Analog Input (Group 30/32)

Group	Var	Type	Description
30	1	Static	32-bit With Flag
30	2	Static	16-bit With Flag
30	3	Static	32-bit Without Flag
30	5	Static	Single-precision (f32) With Flag
30	6	Static	Double-precision (f64) With Flag
32	1	Event	32-bit Without Time
32	3	Event	32-bit With Time
32	5	Event	Single-precision Without Time
32	7	Event	Single-precision With Time

Counter (Group 20/21/22)

Group	Var	Type	Description
20	1	Static	32-bit With Flag
20	2	Static	16-bit With Flag
20	5	Static	32-bit Without Flag
21	1	Frozen	32-bit With Flag
21	5	Frozen	32-bit With Flag and Time
22	1	Event	32-bit With Flag
22	5	Event	32-bit With Flag and Time

Analog Output (Group 40/41/42)

Group	Var	Type	Description
40	1	Status	32-bit With Flag
40	2	Status	16-bit With Flag
40	3	Status	Single-precision With Flag
41	1	Command	32-bit ← DataType=Int32
41	2	Command	16-bit ← DataType=Int16
41	3	Command	Single-precision ← DataType=Float32
41	4	Command	Double-precision ← DataType=Float64
42	7	Event	Single-precision With Time

3) Scan Semantics: Integrity vs Event

Driver will periodically execute:

• Integrity Scan: Acquire "Full Snapshot" (Class 0/1/2/3)
• Event Scan: Acquire "Event Changes" (Class 1/2/3)

The difference depends on Outstation configuration and whether data points support event reporting.