1. Protocol Introduction

DL/T 645 is a common protocol for domestic energy meters/multi-function meters, typical versions are DL/T 645-1997 and DL/T 645-2007 (Most common in the field). The protocol often runs on RS-485, and also often converted to TCP via serial server.

The goal of NG Gateway DLT645 driver is: Stably poll multiple meters on one bus, and decode readings corresponding to DI into unified NGValue.

2. Configuration Model

2.1 Channel Configuration

One RS-485 bus (or one TCP serial server connection) is modeled as a Channel.

2.1.1 version (Protocol Version)

• DL/T 645-1997
• DL/T 645-2007

Version affects

• DI length (1997: 2 bytes; 2007: 4 bytes)
• Control code and some semantics

2.1.2 connection.kind (Connection Type)

• Serial: Serial/RS-485 (Recommended for direct connection to 485 bus)
• Tcp: TCP (Serial server/Gateway)

Serial Parameters (When connection.kind = 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.kind = Tcp):

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

2.1.3 Advanced Parameters

• maxTimeouts: Trigger reconnection after consecutive timeouts exceed this value (Default 3)
• wakeupPreamble: Send preamble wakeup code (Default [0xFE,0xFE,0xFE,0xFE])

Best Practice

• In RS-485 scenarios, preamble wakeup code is a common compatibility strategy; if field device explicitly does not need it, can be configured as empty array to reduce bandwidth.
• Timeout and Reconnection: Try not to set maxTimeouts to 1 (Prone to jitter reconnection), default 3 is usually more stable.

2.2 Device Configuration

Each Device corresponds to a meter:

• address: Meter address (12-digit number, example 123456789012)
• password: Password (Default 00000000, generally hex string)
• operatorCode: Operator code (Optional)

TIP

For detailed explanation of Address/DI, see DL/T Address Syntax.

2.3 Point Configuration

• di: Data Identifier (2007 usually 8-digit hex; 1997 uses low 16-bit)
• decimals: Decimal places (Optional, used for BCD decoding)

Point's data_type affects forced type conversion and scale after BCD decoding.

2.4 Action Configuration

Action is used to encapsulate a set of "Write Meter/Control/Maintenance Command" operations; Action itself does not carry protocol detail configuration.

• Key Semantics: DL/T 645 control code/DI/decimal places and other protocol details should be configured on Action's inputs(Parameter), i.e., each parameter specifies the function and encoding details via Parameter.driver_config.

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

• functionCode: Required. Function Code as follows:

  Enum Name	Description
  BroadcastTimeSync	Broadcast Time Sync
  ReadData	Read Data
  ReadNextData	Read Next Data
  ReadAddress	Read Communication Address
  WriteData	Write Data
  WriteAddress	Write Communication Address
  Freeze	Freeze Command
  UpdateBaudRate	Update Baud Rate
  ModifyPassword	Modify Password
  ClearMaxDemand	Clear Max Demand
  ClearMeter	Clear Meter
  ClearEvents	Clear Events

• di: Optional. Some actions need to specify DI (e.g., "Write a data item"); actions not needing DI can omit.

• decimals: Optional. Decimal places for numeric BCD encoding/decoding (Default strategy see table below).

3. Data Type Mapping Table

3.1 Point (Uplink) Recommended Mapping

Most DL/T 645 readings are BCD (0x33 offset removed):

• Driver will first BCD → f64, then force convert according to Point's data_type, and apply scale (if configured).
• decimals controls BCD decoding decimal places (Default strategy: Numeric defaults to 0 or 2, see table below).

DataType	Recommended Scenario	Decoding Rule (Implementation Semantics)	Remark
Float32 / Float64	Most "Readings/Energy/Power/Voltage" etc.	BCD → f64 → Float (Apply scale)	Most Recommended, least prone to pitfalls
Int8/16/32/64	Field explicitly signed integer reading	BCD → f64 → Integer (Apply scale)	Watch for overflow and decimal places
UInt8/16/32/64	Count/Sequence/Unsigned reading	BCD → f64 → Unsigned Integer (Apply scale)	Watch for overflow
Boolean	Status bit/Switch (Implemented as bit0)	payload[0] & 0x01 != 0	Only suitable for data items with clear 0/1 semantics
String	Meter returns printable text	Try UTF-8/ASCII; trim trailing 0; fallback Binary on failure
Binary	Raw bytes	Raw bytes	Use when unsure of encoding or upper layer parsing needed
Timestamp	Use with caution	Current implementation treats BCD value as timestamp numeric value and force converts (i64 ms)	If device returns "YYMMDDhhmmss" format, do not use Timestamp; please use String/Binary and convert on edge side

3.2 Action Parameter (Downlink) DataType Selection (Write Encoding)

DL/T 645 action write uses Dl645Codec::encode_parameter_value, with explicit whitelist for DataType:

Parameter.data_type	Supported	Default decimals	Encoding Rule
Float32 / Float64	✅	2	Numeric → BCD (Signed)
Int8/16/32/64	✅	0	Numeric → BCD (Signed)
UInt8/16/32/64	✅	0	Numeric → BCD (Unsigned)
Boolean	✅	-	0x00 / 0x01
String	✅	-	Raw bytes (UTF-8/ASCII)
Binary / Timestamp	❌	-	Driver returns config error

Best Practice

• Write value range must be clear: DL/T 645 Action write does not automatically apply scale (scale is Point metadata); you need to write the value expected by the device directly (and control BCD decimal places with decimals).
• Use Float if possible: Prefer Float32/Float64 for reading points, reducing problems caused by "Integer Overflow/Truncation/Decimal Places".