The Case for CAN XL in 10 Mbit/S In-vehicle Networks

CAN XL has recently emerged as a contender in the 10 Mbit/S in-vehicle network space, along with 10Base-T1S Automotive Ethernet. What does CAN XL bring to earn its place on the vehicle bus?

CAN XL builds upon the foundation of CAN and CAN FD, both protocols with a long history in the automotive industry. Figure 1 summarizes the characteristics of the three CAN variants.

Figure 1. A comparison of the characteristics of CAN, CAN FD and CAN XL.

CAN XL increases throughput with a Fast Mode bit rate of 20 Mbit/S in the data phase, while it operates at 1 Mbps in the arbitration phase (those fields other than data). Another feature contributing to the improved bandwidth of CAN XL is the increased data field maximum length of 2048 bytes compared to 64 bytes for CAN FD and 8 bytes for classic CAN.

The Evolution of In-vehicle Network Architectures

The drive for fuel-efficient and safer vehicles opened the door to electronic control in vehicles, which in turn led to the deployment of In-vehicle Networks (IVN).  IVNs have become the backbone of modern vehicles. The volume of data flowing through these networks is increasing exponentially with demands for electric vehicles, advanced driver assistance systems (ADAS), radar, lidar, infotainment systems, cameras and vehicle-to-vehicle communications systems.  

To meet this need, the automotive industry—working with technology suppliers—has developed specialized communications protocols and application-specific extensions to existing network technologies, standardized under the aegis of organizations like ISO and IEEE, and it continues to investigate new topologies and protocols to improve performance, increase reliability and lower the costs of IVNs. Two recent developments have filled a longstanding gap in IVN architectures: CAN XL (up-to-20 Mbit/S extended length CAN) and 10Base-T1S (10 Mbit/S single-pair Ethernet), both of which operate in the 10 Mbit/S network space. What problems do these protocols solve and what opportunities do they present for IVN design?

TDME Primer: Serial Trigger and Sequence Mode Sampling

Figure 1: Sequence mode sampling packs multiple acquisitions
into memory with very little “dead time” between them.

Sequence mode sampling, also referred to as segmented acquisition, is a sampling mode that divides the oscilloscope’s acquisition memory into a user-defined number of equal length segments. Each segment stores a single acquisition of the triggering event, with as much buffer zone as will fit into that segment, given the total number of segments requested. Only after all segments have been acquired is the data processed and displayed. 

The real power of sequence mode becomes evident when you combine it with intelligent triggers, such as the serial data triggers delivered with TDME options. 

TDME Primer: Selecting Sample Rate for Serial Bus Analysis

Figure 1. Sample rate of only four sample points per bit
decodes correctly and lengthens serial bus acquisition.

Teledyne LeCroy supports trigger, decode, measure/graph, and eye diagram (TDME) software options for over 20 serial data standards, and the list is growing. This series will address practical tips for using TDME software successfully, and showcase some examples of applying TDME capabilities to real-world problems.

Given the wide range of protocols supported, you might be curious about how to best choose the oscilloscope sampling rate for a given standard when acquiring serial data signals. The optimal sample rate is determined by three principal factors: 

1) the bandwidth of the signal being digitized by the oscilloscope’s analog-to-digital converter (ADC);

2) the desired duration of the acquisition;

3) what you are going to do with the acquisition.

Why Automotive Ethernet?

Figure 1: The MOST infotainment protocol offers a higher
aggregate bandwidth than Automotive Ethernet, but its 150-Mb/s
bandwidth is shared across the network

In recent posts, we've been reviewing the subject of Automotive Ethernet in general and the BroadR-Reach protocol in particular. In today's installment, let's look at some of the benefits of using the protocol while comparing it to some other protocols that see usage in the automotive environment.