IEC 61162-2:1998

Overview

IEC 61162-2:1998 specifies a high‑speed one‑way serial digital interface for maritime navigation and radiocommunication equipment. Intended for single talker / multiple listeners arrangements, it defines electrical, wiring and data format requirements for transmitting printable ASCII sentences (based on NMEA 0183 v2.30) over a balanced differential link. The standard supports high-rate transmission (38 400 bit/s, 8N1) for short messages (typical 11 to 79 characters) with repetition intervals down to ~20 ms.

Key topics and technical requirements

• Topology: one talker driving multiple listeners in parallel; no provision for multiple simultaneous talkers.
• Physical cabling: shielded two‑conductor twisted pair (lines A and B) plus a common/signal ground (C); recommendations and rules for single/double shields and continuous shielding to meet EMC requirements.
• Electrical characteristics: compliant with ITU‑T V.11 (balanced differential signalling) with compatible drivers (e.g., EIA‑485 allowed if used compatibly). Signal polarity: idle/mark defined as negative voltage on A vs B. Receive circuits must be isolated per IEC 60945.
• Data transmission: asynchronous serial, 38 400 baud, 8 data bits, no parity, 1 stop bit; characters are 7‑bit ASCII in an 8‑bit field (D7 = 0).
• Data format: printable ASCII sentences (NMEA-style), fields and sentence structure defined; typical sentence lengths and repetition rates documented.
• Reliability and safety: limited error checking and no guaranteed delivery - the standard cautions against using it alone for safety‑critical functions.
• Manufacturer documentation: products claiming compliance must document signal line identity (A/B/C), output drive, approved sentences, latencies, listener load, connector details, and software/hardware revision.

Practical applications

• Interfacing onboard navigation instruments (GPS, AIS receivers, heading sensors, echo sounders) where a single source broadcasts data to multiple consumers (displays, autopilots, chart plotters, logging systems).
• High‑rate data feeds where the simplicity of one‑to‑many serial distribution is preferred over complex networks.
• Retrofit or interoperable installations using established NMEA 0183 sentence formats but requiring higher baud rates and balanced signalling for improved noise immunity.

Who should use this standard

• Marine equipment manufacturers implementing serial talker outputs or listener inputs.
• System integrators and shipyards wiring shipboard navigation and communication systems.
• Test labs, certification bodies and designers verifying interface compliance and EMC behavior.

Related standards

• IEC 61162‑1 (single talker/multiple listeners, lower speed)
• IEC 60945 (general maritime equipment requirements)
• NMEA 0183 v2.30 (sentence format alignment)
• ITU‑T V.11 and EIA‑485 (electrical signalling references)

Using IEC 61162‑2 enables reliable high‑speed one‑way distribution of navigational data when designers follow its wiring, electrical isolation and documentation rules - while noting its limits for safety‑critical applications.