The CiA 443 CANopen profile for Subsea Instrumentation Interface Standardization (SIIS) level-2 devices specifies communication interface specifications for simple sensors, multi-functional meters, and valves. Since version 4.0, the document also considers battery cell assemblies, voltage converters, as well as the required unit for battery management. The default physical layer is ISO 11898-3 compatible. The default bit rate is 50 kbit/s. Optionally, the CAN physical layer according to ISO 11898-2 can be used. The CANopen node-ID is assigned via layer setting services (LSS, see CiA 305). The profile specifies a bootloader mode, and the starting and stopping of application programs. Simple sensors include pressure, temperature, and position sensors as well as inclinometers. The profile also supports multi-phase flow, wet-gas, oil-in-water, and some other complex meters as well as dedicated detectors (e.g., PIG: pipeline inspection gauge). There is no mapping defined for the four default TPDOs (transmit process data objects) and RPDOs (receive process data objects). The PDO communication parameters are pre-defined.

Offshore oil rigs require communication networks for being well informed at any time, e.g., about the conditions around the drilling hole. The Subsea Instrumentation Interface Standardization group (SIIS group) has introduced three levels of communication networks. SIIS level 3 networks cover the Ethernet-based communication between the oil rig and the CANopen-based SIIS level-2 networks, installed on the ocean ground. On the deeply embedded level, the SIIS level-1, there are discrete analog interfaces. SIIS-level 2 networks, which are in the focus of CiA 443, comprise redundant controllers, different sensors, valves, and other equipment. CiA 443 has been developed and maintained in cooperation with the SIIS group.

The CiA 443 profile comprises interface specifications for simple pressure and temperature sensors as well as complex multi-purpose instruments such as multiphase flow meters. Subsea actuators defined in CiA 443 include simple valves and valve controller units. Support for layer setting services is mandatory. It is recommended to support the optional LSS identify service.

After power-on, SIIS level-2 devices enter the bootloader mode; application programs are not started automatically. In this mode, heartbeat functionality is not disabled. The device waits for the start command given by the application manager. When an application program is started, the device first performs a local NMT (network management) reset node service. In this operation mode, heartbeat functionality is mandatory. If all application programs are stopped, the device performs a local NMT reset node service and falls back into the bootloader mode.

The specification of the SIIS level-2 application manager is not covered by the CiA 443 profile. It could happen that several manager-capable devices are integrated into the network. For this reason, the NMT flying manager functionality, as specified in CiA 302-2, is considered by these devices.

The CiA 443 profile includes several virtual devices. SIIS level-2 devices may provide a sub-layered network or serial links. In these cases, it serves as a gateway and provides proxies for the connected functions (e.g., different sensors). In this way, SIIS level-1 devices can be easily integrated into SIIS level-2 networks.