Hi
My customer is adopting SN65HVD251. Below waveform is (canH-canL). CAN signal communication frequency is 500KHz. Below fall time is about 1.16us. Is this fall time ok for CAN communication? And what is the spec requirement of Rise/Fall time when CAN communication cycle is T? Thanks!
Regards
David
David,
Each bit for CAN is divided into four sections, shown below:
The SYNC_SEG portion is the time that a recessive to dominant transition is expected to occur, so within 25% of the bit width, the transition from high to low should occur. The bit width in your system is 2us, which means your transition would need to happen within 500ns. It doesn't look like the waveform you are showing is actually hitting the lower threshold at 1.16us, but a bit earlier, closer to the 500-600ns range.
In the CAN spec there actually isn't a specification for rise and fall time, only bit width and propagation delay, so unfortunately there is no equation I can give based on T.
The fall time looks like it is okay to me, but you could definitely make it better by removing some capacitance on the bus. Do you have anything connected to the Rs pin?
Regards,
