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Forum: FPGA, VHDL & Verilog Can protocol to FPGA


Author: Ba Ehb (Company: Université) (ehb)
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Hi,

In my project , I need to adapt an FPGA card to read data from 4 CAN 
network at least. Beacuse i didn't found an FPGA including more than 2 
CAN controllers. i ´m wondering if there is a solution for this. I read 
that is possible to emumate CAN bus with RX TX I/O of the fpga with an 
IP core but i dont't find more information of how it is possible.
Also , i don't know if we can use the protocole CAN only with the GPIO 
of the fpga.

Can any of you guys suggest how to perform this ?


thx

Author: Frank (Guest)
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You have to use an/some IP-Core/s.
For example:
http://www.ifi-pld.de/IP/Advanced_CAN/advanced_can.html

Maybe there are also some free Corey at OpenCores or others.

Author: Ba Ehb (Company: Université) (ehb)
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Thank you for the response.
If i use an Ip core ( i found one in opencores) can I use directly the 
gpio's of the fpga or i have to add an external composant to communicate 
with the protocol can ?

Author: Frank (Guest)
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Ba E. wrote:
> If i use an Ip core ( i found one in opencores) can I use directly the
> gpio's of the fpga or i have to add an external composant to communicate
> with the protocol can ?

I will recommend you a bus tranceiver like this one:
http://www.microchip.com/wwwproducts/Devices.aspx?...

Author: Lothar Miller (lkmiller) (Moderator)
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Ba E. wrote:
> can I use directly the gpio's of the fpga
No, because the CAN interface is much more "analog" than the FPGA IO 
drivers. As already said: you must adapt the different physics by using 
a CAN transceiver. Additionally with a transceiver you get an EMV and 
ESD robust interface too.

Author: Giorgio (Guest)
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Ba E. wrote:
> Beacuse i didn't found an FPGA including more than 2
> CAN controllers.

Do you want to say by that, that there ARE FPGAs with Can Controllers at 
all?

Author: Ba Ehb (Company: Université) (ehb)
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I found an FPGA including two CAN's here :
http://www.devboards.de/en/home/boards/product-det...

Now, with the transeiver that Frank gave, I Have to link a transeiver to 
the FPGA as a CAN bus ? ( for 4 CAN bus , 4 transeivers ? )

Author: Lothar Miller (lkmiller) (Moderator)
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Ba E. wrote:
> I found an FPGA including two CAN's here
Indeed you did find a BOARD with a FPGA and "2 CAN Transceiver" on it. 
There's is NO (in numbers 0) CAN controller inside the FPGA. You 
must implement 2 CAN controllers and connect them to the transceivers.

And when that is done you simply wire two additional transceivers to the 
FPGA (in the same manner as the two on the board). Finally you implement 
two additional CAN cores in the FPGA. Then you're done...

So the very first step is to implement 1 core in the FPGA and connect it 
to 1 of those transceivers.

: Edited by Moderator
Author: Ba Ehb (Company: Université) (ehb)
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Ah okey , I start to understand a little bit what you sayin guys. Really 
thank you.

So I restate my probleme ( I attached a diagram to be clearer ): i want 
my FPGA have 2 inputs of data ( that transmitted in protocole CAN) and 2 
outputs of data ( that will be transmitted ine protocole CAN ) I thought 
that it possible to emulate a bus CAN without adding anything to the 
FPGA only using GPIO's and you said it's not possible. What about the RX 
TX of fpga solution to emulate a CAN Bus ( without adding external 
coposants) ?

Also ,  I don't know if it's possible to use only internal ressources of 
the fpga to emulate can bus ?

Author: -gb- (Guest)
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Hello I got an Spartan3 FPGA Baord with CAN transciever. It is a 
Celoxica RC10. The Original Software is old, but you could use it with 
ISE because it has JTAG. The only manual i foud is here:

https://www.yumpu.com/en/document/view/31620653/rc10-manual

Author: Frank (Guest)
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So if you need 4 independent CAN-Bus lines, then the schematic should 
look like in the attached picture.

Author: Lothar Miller (lkmiller) (Moderator)
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Ba E. wrote:
> i want my FPGA have 2 inputs of data ( that transmitted in protocole
> CAN) and 2 outputs of data ( that will be transmitted ine protocole CAN )
Why do you split that up? CAN is a Bidirectional-Multi-Master-Bus.

> What about the RX  TX of fpga solution to emulate a CAN Bus
Each of the FPGA cores will have a TX output and a RX input. The CAN 
transceiver will make CANH and CANL out of those signals. The CAN bus 
itself is based on CANH and CANL as the physical layer. The IO ports of 
an FPGA is not able to generate those CAN bus signals without additional 
hardware reliably. That starts with the IDLE level which is differential 
0V. Simply startt reading about signal levels on a CAN bus and compare 
them with the capabilities of the IO pin drivers.

> Also , I don't know if it's possible to use only internal ressources of
> the fpga to emulate can bus ?
Do you want to have 4 real physical CAN busses to connect real physical 
devices or do you only want to "emulate" or "simulate" something?

> if it's possible to use only internal ressources of the fpga
No. To get a real CAN Bus with CANH and CANL you MUST use a transceiver. 
Why the heck don'T you simply connect such two transceivers for small 
money to the FPGA. Thats only 4 wires plus supply in total...

-gb- wrote:
> got an Spartan3 FPGA Baord with CAN transciever. It is a Celoxica RC10.
That borad only has 1 CAN transceiver. The DBC5CEFA7 usesd by Ba Ehb has 
2 transceivers. But he wants 4. So what to do?

Frank wrote:
> if you need 4 independent CAN-Bus lines, then the schematic should look
> like in the attached picture
I added to the schematic some signal names for clarity.

: Edited by Moderator
Author: Ba Ehb (Company: Université) (ehb)
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Thank you all for your responses. It's very helpful and it clarified 
things to me.

So , I understand that i have to use transceivers like Lothar Miller & 
Frank said. in the diagram the transceiver is connected to the fpga 
using RX/Tx ports of the Fpga. Now my question is : Is an FPGA have a 
limited numer of RX/TX ports ? ( because if I need 4 Can busses then i 
will use 4 transcievers that will have to be connected to 4 Rx/tx ports 
)

There is an FPGA with like 10 Rx/Tx ports to connect 10 transceivers ? ( 
in reality i need 10 Can busses , i just said 4 to understand )

The Rx/Tx ports of the Fpga are the RS232 port ?

Can the transcievers just be connected to the fpga using GPIO's ?


>Why do you split that up? CAN is a Bidirectional-Multi-Master-Bus.
I don't want t split I just wasn't clear.

Author: Frank (Guest)
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Ba E. wrote:
> Can the transcievers just be connected to the fpga using GPIO's ?

Yes of course!
You have to connect the internal IP Core ports to physical GPIOs of your 
FPGA with your preferred description language (VHDL, Verilog, ...).

There are no special physical Rx/Tx ports you have to usw.

Author: Lothar Miller (lkmiller) (Moderator)
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Ba E. wrote:
> The Rx/Tx ports of the Fpga are the RS232 port ?
No. As already stated the RX and TX are signals on simple IO pins of the 
FPGA. And there is no kind of RS232 port involved in the whole system at 
all. That mentioned RX and TX signals are the receive input and the 
transmit output of the CAN IP core inside the FPGA. Every (or at least 
nearly every) IO pin of the FPGA could be RX or TX...

> There is an FPGA with like 10 Rx/Tx ports to connect 10 transceivers ? (
> in reality i need 10 Can busses , i just said 4 to understand )
As I already said: implement ONE (in numbers 1) CAN interface. Then have 
a look how much resources it needs in the FPGA. Then have a look for a 
FPGA that provides at least 10 times that resources (plus some more or 
less demanding logic you will need additionally to serve those 10 CAN IP 
cores).

But first start with 1 CAN interface. Thats the very first step.


BTW: why in all the world do you need a node with 10 CAN interfaces in 1 
design?

Author: Rhonn 71 (Guest)
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Hello Everyone!

We are on stage of developing CAN controller, could anyone help us for 
any suggestions on how we can achieved this? Like useful sites, or 
existing VHDL codes so that we can have some basis for our design. Also, 
we only have FPGA as our hardware for implementation.
We appreciate your responses.

Thank you very much!

and regards!

Author: berndl (Guest)
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Just search for "bosch d-can" or have a look at open-cores...

Author: Michael (Guest)
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Or you can connect 10 SJA1000 or MCP2515 to the FPGA?

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