by Mike Donnelly
1 March 2018
Ever since the CAN specification was released many decades ago, designers have pushed their network configurations beyond the conservative limits of the standard, driven by manufacturablity, customization flexibility and other non-technical reasons. With thorough engineering analysis, including electrical simulation of the physical layer, they were able to design communication systems that meet both demanding performance and economic requirements.
The lastest advance in the CAN standard, Flexible Data Rate (or CAN FD) is an approach to extend the data throughput capabilities while re-using the existing physical-layer infrastructure. By using existing bit-rate limits for the CAN message frame, but using higher rates for the message data, the information transfer rate can be significantly increased. But engineering analysis is needed to assess network performance and signal quality at both data rates, as well as during the transition to overdrive!
This "Live" 4-node CAN (FD) network can be used to verify signal quality for various network configurations specified by the reader. Many of the component parameters can be modified to represent network variants. This includes transmission line lengths, termination impedances, transceiver drive strengths and edge-rates, the selection of the transmitter node, as well as the test data rates to be used*. (Go ahead, try it yourself, just double-click on a component with a blue parameter value, change that value and press the green "play" (simulate) arrow. The results of your change will soon be visible! It is particularly interesting to increase the length of one of the stub lines, for example the transmission line going to node2 in the lower left, from its nominal 1 meter value to perhaps 10 meters. This will cause a complete collapse in data communications ... just look for bit errors in the upper wave viewer)
If you open this design in PartQuest Explore and save it as a new copy, then you can free-form edit the network topology, adding new nodes, transmission lines and other passive or active components. New simulation runs will help you assess the viability of those network configurations.
We hope you find our network analysis capability to be helpful, as you push the limits of CAN to meet your network performance requirements.
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*Note: The transmit-enable bit for any node can be changed by setting the corresponding "Set Level" logic_value to either '1' (transmit) or '0' (receive only). The user can also specify the "slow" and "fast" data rates, as well as the number of bits to be sent at each rate, on the CAN FD data source (u1, bottom middle). A series of these slow and then fast random data bursts continue until the end of the simulation time.
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