RE: Fwd: Query: CAN

Hi Gaurav,
Most of your questions are more like the ones someone taking a course in
communications would ask.  In the practical world interfacing to various CAN
devices one doesn't really care if it's NRZ or RTZ or in the case of CAN NRZ
with bit stuffing.  Same with whether there's a clock.  They would just
select a driver to attach to their CAN device.

For the communications bus at one time they chose the only available bus
driver (82C250)  or before that used a resistor network with the drivers on
the 82C200 and went on with encoding the application.  But now there are a
large number of CAN bus drivers available and more coming with CAN_FD.

Similarly in an instrument panel I doubt that the connections between the
various gauges and indicators would use DB-9 connectors as they are too
expensive and bulky.  Especially if you were designing a high end very
expensive super car and all devices share the same battery power and ground.


As suggested in other posts your first step is to acquire a few data sheets
or specification sheets that describe CAN messaging.  Pay particular
attention to what is called CSMA/CR where the CR stands for Collision
Recovery.    Understanding how the arbitration works within the CAN protocol
will go a long way into understanding why the bus drivers are designed the
way they are.

Do a search on CAN bus drivers and download each data sheet.  Most will
appear to be the same but there are some that provide functionality if:
1. The node is no longer powered but still connected to the bus.
2. As standard CAN is a 3 wire bus system what happens if the Ground is
lost.
3. What happens if CAN_L or CAN_H are lost.
4. What if some systems are 3V and others are 5V.

John Dammeyer

> From:"Gaurav Mishra" <[email protected]>
> Date:Sun, 12 Jul, 2015 at 10:26
> Subject:Query: CAN
> 
> Hello,
> 
> 
> I am Gaurav. I am a recent graduate in Electronics and have been working
> with an Automotive Company for a few months.
> 
> My job requires me to code applications for Low,Mid/High Range of
> Instrument Cluster Panels for CAN Based networks.
> 
> 
> I've recently acquired information about this mailing list and have been
> advised to direct my CAN based queries here.
> 
> 
> Can anyone please help me with the following questions?
> 
> What is the specific advantage of using NRZ encoding scheme over other
> coding schemes for CAN ?
> I am also hoping to understand that why the designers did not opt for a
clock
> based sync as with other serial communication protocols ?At my workplace,
> we use a DB-9 connector with the following configuration:
> 
> o   Pin 2 : CAN LOW
> 
> o   Pin 3 : GND
> 
> o   Pin 7 : CAN High
> 
> o   Pin 9 : CAN V+
> 
> What really is the significance of each of these? i.e. if i take one out,
what
> happens to the network ?
> 
> 
> Kindly ignore any naivety in the above query. Also kindly forward any
> related link with the above.
> I might've skipped that.
> 
> 
> Thank you for your time.
> 
> 
> Best Regards
> 
> Gaurav Mishra
> 
> -------------------------------------------------------------
> --
> mit freundlichen Grüßen
>        Heinz-Jürgen Oertel
> --
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