Contents
CAN bus termination wattage?
The most conservative approach would be 4.8W which will allow for a CANH or L short to the power supply and the other bus pin to GND. This also covers a similiar bus line short to 24V and a software or PCB fault driving D low permanently.
How many ohms are terminators?
In general, majority of the equipments have 50 Ohm impedance. But for video signals 75 Ohm impedance matching is essential to avoid distortion of the signal. There are two major types of coaxial cables terminators: BNC type and F type. The BNC type has both 50Ω and 75Ω impedance, while the F type has 75Ω.
CAN hard synchronization?
Hard synchronization occurs on the recessive-to-dominant transition of the start bit. The bit time is restarted from that edge. Resynchronization occurs when a bit edge doesn’t occur within the Synchronization Segment in a message.
What does a 60 ohm bus termination resistor mean?
Any value lower than 60 Ohm indicates that there are probably more than two 120 Ohm bus termination resistors present (resp. configured). A value bigger than 60 Ohm typically indicates that there is at least one bus termination resistor missing or the bus terminators have a wrong resistance value.
How is a CAN bus termination wire installed?
The bus termination might be installed by external 120 Ohm resistors placed in between the “CAN High” and “CAN Low” wire at both end points of the network (like shown by the picture above). Some CAN devices offer internally installed bus terminators which can be switched on / off easily.
How many resistors are needed for a CAN bus?
It is important that there are just two bus termination resistors installed or configured in a CAN network. This can be checked easily by powering down all CAN devices and measuring the resistance in between the “CAN High” and “CAN Low” wires. The measured resistance must be approximately 60 Ohm.
Why is there a 120 ohm bus impedance?
Why it’s 120 is simply a function of the design limited by physical size. It isn’t specifically important which value they picked within a broad range (for example, they could have gone with 300 Ohms). However, all devices in the network have to conform to the bus impedance, so once the CAN standard was published there can be no more debate.