Overview
ISO 16844-4:2022 - Road vehicles - Tachograph systems - Part 4: Display unit communication interface - defines the CAN-based communication between a tachograph display unit and other devices on an SAE J1939-based in-vehicle network. The standard specifies requirements and recommendations across the physical, data link, network and application layers (OSI model) and lists the supported parameter groups used for exchanging tachograph-related data.
Key Topics and Technical Requirements
- CAN physical layer: Compliance with SAE J1939-11 (250 kbit/s) and SAE J1939-14 (500 kbit/s); CAN cabling/termination out of scope.
- Bit-timing: Single-sampling mode with a sample point between 80% and 88% of nominal bit time; explicit timing parameter ranges are provided for 250 kbit/s and 500 kbit/s operation.
- Data link layer: Conformance with ISO 11898-1; only Classical Extended Frame Format (CEFF) frames are allowed; remote frames prohibited.
- Transport layer: Support for SAE J1939-21 transport protocols, including BAM and TP.DT for multi-frame transfers.
- Application layer: Based on SAE J1939-21 and SAE J1939-71 rules. Specifies required and optional parameter groups (PGs) and message handling behaviours.
- Mandatory supported messages: time/date (TD), vehicle identification (VI), high-resolution vehicle distance (HRVD), service information (SERV), reset (RESET), tachograph (TCO1), driver identification (DI), time/date adjust (TDA), and electronic engine controller 1 (EEC1).
- Optional messages: cab illumination (CL) plus additional PGs listed in Clause 9.
- Parameter encoding rules: Multi-byte parameters use LSB in the lower byte position; ASCII strings transmit the first character first; parameter definitions are specified in ISO 16844-7.
- Acknowledgement semantics: Control-byte values defined (e.g., 0 = positive ACK, 1 = negative ACK, 3 = cannot respond now).
Applications
- Ensuring interoperability between tachograph display units and vehicle ECUs on SAE J1939 networks.
- Guiding firmware development for display units, data loggers, telematics and maintenance tools that access tachograph data.
- Supporting compliance testing and validation of in-vehicle communications for tachograph installations.
- Enabling consistent data access for drivers, transport operators, workshops and enforcement authorities.
Who Uses This Standard
- Tachograph and display unit manufacturers
- Vehicle OEMs and ECU suppliers
- Telematics and fleet management integrators
- Test labs, homologation bodies and regulators
- Workshops and service tool developers
Related Standards
Keywords: ISO 16844-4, tachograph, CAN, SAE J1939, display unit communication interface, vehicle networks, parameter groups, PGN, transport protocol, vehicle telematics.
