Some thoughts about differential buses RS 485, CAN, USB

Hello,

For a next project, i am trying to sniff with the same IC a number of differential busses: RS485, CAN and hopefully USB.

I am not interrested in the higher layers of the communication. I just want to convert the differntial signaling to logic levels that can be interpreted by an FPGA.

I was thinking of using this IC : https://www.electro-tech-online.com/custompdfs/2012/09/am26ls32a.pdf (I like this IC because it can take +/- 25V on differential input pins, making is suitable for work in hazardous situations...)

Now, here is my question:
It seems to me as if RS485, CAN and USB use very similar signaling. At least, from the receiver point of view. Is that correct? Am i missing something..?

Thank you very much!

Have been making some reading here and there. As Wiki says (https://en.wikipedia.org/wiki/CAN_bus), the driving of CAN is quite different than RS485; I am aware of that, but still, from the receiver point of view, i can't seem to find any difference...

Can any one confirm..?

I will be doing some tesing monday at the office and will let you know if you are interrested

CAN, RS485 and USB are all fully differential when transmitting data. USB has an additional state SE0 (both lines low).

Thanks Dougy83.

Ok let's drop USB, what about just CAN and RS485. Can i assume from your comment that they are compatible in terms of reception..?

The CAN bus seems to be more a protocol layer definition. It seems the physical layer is somewhat weakly defined and each car maker has their own way of defining the connector and hardware. From what I did find on the 9 pin definition, the voltages between the CAN and 485 seem to be slightly different.

A CAN receiver IC, e.g. https://www.electro-tech-online.com/custompdfs/2012/09/AMIS-30663-DPDF.pdf should be able to handle reception of both RS485/422 and CAN. The CAN transceiver shown has a very large permissible input voltage range, which RS485/422 receivers may not possess.

Both protocols are differential, RS485 has a minimum differential threshold of 200mV (I think... from memory) while the CAN IC shown requires ~0.7V difference. RS485 will be well above this level unless severely attenuated