CAN Bus "Bus-Off error" EMX

[NemesisXB]

@Dave McLaughlin

Looks like you use Altium Designer (Protel)

Yes, Altium Designer 10. Best Layout software I’ve used by far. Waiting for my boss to buy me 2013.

@Dave McLaughlin

Check page 9 and you will see that the CANH and CANL are only active when the transmit input is greater than 3.8V. This would confirm why you are not seeing anything on the bus when using 3.3V logic. The SN65HVD230 is 2V from what I can see.

Dave, I believe you misread the datasheet. It states that CANH and CANL is disabled while VDD < 3.8V, not the transmit input. On page 10 the VIH (High level input voltage) for the TXD pin is specified as 2.0V. I am however also leaning towards the 3.3V being the problem, but on the other hand, I have the same design on the other board, also with a LPC processor powered from 3.3V and that works perfectly. So I don’t understand why the 3.3V would be a problem.

@Dave McLaughlin

PS. One thing I don’t see on your schematic is decoupling on the supply at the IC. I am assuming that this is located elsewhere on the design and just not shown in your image you posted? You would be surprised at what works and doesn’t work with this missing. Anyway, I believe you have these.

Yes, I do have them. I’ve learned my lesson on this one a long time ago. Just FYI, I even have a super cap on this board, so my power rails should be pretty clean.

[Dave_McLaughlin]

Hi

I just bit the bullet and went back on maintenance and I am running AD13 alongside AD10 until I am comfortable with it but so far so good. I love the 3D modelling ability and I now get almost 100% mechanically fitting designs because I can export to CAD and check it. Just need to get the electronics part working 100% and I am good to go

i see what you mean on the 2V but from what I read, you need 3.8V to enable the bus. You said you are not seeing any activity on the bus?

It certainly does not explain why the same device works on another 3.3V design. Did that have a pullup on the TXD line? I assume the EMX is 5V tolerant. What about trying a pullup to 5V just as a quick test?