CAN Newsletter magazine
CAN FD SIC (signal improvement capability) transceivers compliant with CiA 601-4 are able to remove some limitations and accelerate CAN FD far beyond that what was previously possible.
The complete article is published in the December issue of the CAN Newsletter magazine 2019. This is just an excerpt.
While CAN FD was defined up to 5 Mbit/s in the data phase, a speed limit was encountered when networks were evaluated. Especially in recessive bits, two topology effects cause limitations: signal ringing, caused by not terminated stubs and signal plateaus, created by lower characteristics cable impedance. These two effects disturb the signal at the beginning of the recessive bit and they delay it from becoming stable before the sample point.
The CiA 601-4 document specifies a receiver-based and a transmitter-based approach. NXP implemented the activation of the ringing suppression on the TXD input, which is both reliable and allows a significantly faster activation time, since this triggers the signal improvement even before the internal propagation delay of the transceiver. The article discusses in detail the benefits and tradeoffs. It also explains the necessary transceiver symmetry. There are also some limitations regarding the arbitration phase to be considered.
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