The sample point is the location, typically given as a percent value, inside each bit period where the CAN controller looks at the state of the bus and determines if it is a logic zero (dominant) or logic one (recessive). All CAN controllers allow this point to be configured and it is always specified as a percentage from the start of the bit period.
The location of the sample point is a trade-off. An early sample point decreases the sensitivity to oscillator tolerances and allows lower-quality oscillators. A late sample point allows for a longer signal propagation time and therefore a longer bus. A later sample point is useful for non-ideal bus topologies.
The CAN-in-Automation user’s group makes recommendations of where the sample point should be for various bit rates, with 87.5% the most common.
"FAQ contribution from Embedded Systems Academy, experts in CAN bus. For more information visit www.esacademy.com"
