Electronic Design
Automotive Ethernet Arrives

Automotive Ethernet Arrives

The OPEN Alliance (One-Pair Ether-Net) Special Interest Group has released their standard for in-vehicle Ethernet over a single twisted pair (Fig. 1). The OPEN Alliance includes two automotive companies, BMW and Hyundai USA, plus three semiconductor companies including Broadcom, Freescale and NXP.

OPEN fills a gap between CAN, LIN and FlexRay that are used automotive control and MOST (Media-Oriented Systems Transport), a high-end multimedia network (see MOST: The Automotive Multimedia Network). MOST uses fiber optics and runs at speeds up to 150 Mbits/s. It is a standard 10/100 Mbits/s Ethernet but it uses only a single, unshielded twisted pair cable comparable to that already used by FlexRay. Better yet, it is possible to deliver power over the same two wires like Power-over-Ethernet (POE). This is definitely a game changing approach because it is suitable for a range of applications throughout the car (Fig. 2) from On-Board Diagnostics (OBD) to advanced driver asistance (ADAS) applications (Fig. 3).

The standard defines new PHYs that connect to standard Ethernet MACs. This means that existing microcontrollers with an Ethernet Media Access Controller (MAC) with a Media Independent Interface (MII) can be mated to an OPEN PHY. There are no special drivers or protocols to incorporate. The system works equally well with any standard Ethernet device including those using protocols like IEEE 1588 clock synchronization.

The standard supports the standard Ethernet audio/video bridging (AVB) standard, 802.1BA. It also address temperature and EMC details that are critical to automotive applications. OPEN will be suitable for use anywhere on the car from the engine compartment to doors. Hardware can be qualified for Automotive Electronics Council (AEC) AEC-Q100.

Cable length is limited to 47m. A typical automobile would need no more than a 30m limit but this allows the technology to be used in larger vehicles. The technology can work with significantly longer cables up to about 500m.

OPEN Ethernet mirrors standard Ethernet that is essentially a switch-based interconnect. This is key because bandwidth is less of an issue assuming a single application can be handled by a link. It is even possible to combine multiple links to provide higher bandwidth but this would be less likely given the drive to use a single cable to reduce costs.

In theory, the new Ethernet approach can reduce connectivity costs by up to 80% and reduces cabling weight by up to 30% compared to a conventional Ethernet LVDS interconnect. OPEN Ethernet can use connectors like those approved for FlexRay. This is important because, at least initially, automotive vendors are likely to use their own approved connectors and cabling.

Still, standard cables and connectors could be useful. For example, a four camera ADAS (advanced driver assist) application would be less expensive if the cameras were a standard component. There is already a standardization effort for automotive cameras. All it would need to incorporate would be a standard OPEN connector. But that is for the future.

Right now the semiconductor participants are delivering chips to handle the new standard. Broadcom's BroadR-Reach family includes a set of PHYs and switches. There are three switches with a mix of built-in PHYs. These include the 7 port BCM89500 with 4 OPEN PHYs, the 7 port BCM89501 with 5 PHYs, and the 4 port BCM89200 with 2 PHYs. The ports without PHYs can be connected to devices or external PHYs. The BCM89810 is a standalone BroadR-Reach 10/100 PHY. This is the PHY that would be used with microcontrollers. In the future, this kind of PHY might be incorporated directly into a microcontroller.

Also part of the mix is Broadcom's BCM89610 10/100/1000 PHY. This is a conventional Ethernet PHY optimized for automotive use. A single BCM89610 could provide a link to an external diagnostic system. The chip has the same EMC resistance as the other BroadR-Reach.

The OPEN Alliance and its members are targeting automotive applications but the technology is ideal for a host of other application areas from robotics to home security systems. Ethernet is already in demand in these applications and a two-wire solution with power easily beats existing technology in cost.

Ethernet has had a long and fruitful life becoming the dominant interconnect for a very wide range of applications. It could now become the dominant interconnect for automotive applications as well.

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