CAN Bus-Identification - Electronic Circuits Projects Diagrams Free

Sathiesh Kumar · 3rd November 2009, 12:24 AM

Hi,

I have a doubt whether CAN Bus is a normal wire which can be used with CAN Protocol or whether its a specially designed bus...

Can any one help me...

Sathiesh Kumar.V

Papabravo · 3rd November 2009, 02:06 AM

CAN can use any kind of wire you like. It is only if you want to push the limits of the technology that special purpose cabling is used. In the special purpose network cables used for CAN, the cables are characterized and the values are consistent from one spool to the next.

Oznog · 3rd November 2009, 06:40 AM

CANbus is by definition a differential pair, essentially two wires plus ground. They generally need to be a twisted pair.

Assuming this is PIC, the PIC's CANbus implementation requires a simple CAN transceiver chip. You might think you can take the CAN Tx out of one PIC and feed it into the CAN Rx of another chip and vice versa, but no, that's impossible. Unlike the UART, the CAN protocol will not support this type of connection.

Sathiesh Kumar · 3rd November 2009, 11:48 AM

Then how the connections has to be made between two nodes...

Papabravo · 3rd November 2009, 02:02 PM

Quote:

Originally Posted by Oznog

CANbus is by definition a differential pair, essentially two wires plus ground. They generally need to be a twisted pair.

Assuming this is PIC, the PIC's CANbus implementation requires a simple CAN transceiver chip. You might think you can take the CAN Tx out of one PIC and feed it into the CAN Rx of another chip and vice versa, but no, that's impossible. Unlike the UART, the CAN protocol will not support this type of connection.

Some CAN controllers may be connected together on a single board, because they have differential inputs and outputs. Examples are the 82C200 and the SJA1000. The OP's question was about the wire. I have used untwisted hookup wire and speaker cable to make "short" networks. For installations we used specialized cables with foam dielectric, individually foil shielded, with a drain wire, and an outer braid jacket.

Oznog · 3rd November 2009, 08:33 PM

What are you trying to connect? A PIC with a CANbus port, or CAN controllers, or what?

NHN · 3rd November 2009, 09:00 PM

I've used some basic .35-.5mm electrical wiring for canbus in my car mate, cat5 stranded network wiring will do I should think no?

Papabravo · 3rd November 2009, 10:51 PM

Quote:

Originally Posted by NHN

I've used some basic .35-.5mm electrical wiring for canbus in my car mate, cat5 stranded network wiring will do I should think no?

Almost anything will work for a short network. On a long network there are at least two things to watch out for.

Transmit levels for a dominat bit vs. Receiver thresholds for a dominant bit
Reflections at high baudrates affecting the voltage level at the sample point.

Oznog · 4th November 2009, 04:16 AM

CANbus should be wired in a line, with no "star" branch connections. And the ends must be terminated with a specified resistance to avoid causing reflections back down the bus.

Papabravo · 4th November 2009, 05:52 AM

Quote:

Originally Posted by Oznog

CANbus should be wired in a line, with no "star" branch connections. And the ends must be terminated with a specified resistance to avoid causing reflections back down the bus.

Mostly nonsense. Trunkline/dropline is a perfectly reasonable toplogy for a "long" network of say 500 meters @ 125KBaud with drops up to 3 meters. On a very short(<1Meter) network you want only a single terminator equal to the parallel combination of the terminators you would use on the long network, since reflections are no problem at all.

Oznog · 4th November 2009, 07:18 AM

I'm just going by what is stated in the CANbus specification. I do distinctly recall that branches were a no-no (but that's not saying it'll always be a problem), and that the end of the string needed termination.

atferrari · 4th November 2009, 07:29 AM

In real circuits I hade the chance to see, short stubs are common. I personally understand that "adding" nodes would be impractical if the "line" should be extended for every newcomer to the already working circuit.

I admit my lack of practical experience other than having worked out a running CAN network with three PICs on my bench.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar
Title	Starter	Forum	Replies	Latest
device identification	thaithanh	Datasheet/Parts Requests	12	16th October 2008 01:43 AM
Diode identification	shahbaz.ele	Datasheet/Parts Requests	6	15th October 2008 01:46 AM
IC Identification	johnsmith123	General Electronics Chat	4	14th October 2008 02:32 AM
Lead Identification	GoKid	General Electronics Chat	5	23rd June 2006 04:06 PM
transmission of data from a moving bus to a bus station	sammy	Electronic Projects Design/Ideas/Reviews	2	25th October 2003 12:59 PM

3rd November 2009, 12:24 AM	#1
Sathiesh Kumar	CAN Bus-Identification Hi, I have a doubt whether CAN Bus is a normal wire which can be used with CAN Protocol or whether its a specially designed bus... Can any one help me... Sathiesh Kumar.V

3rd November 2009, 02:06 AM	#2
Papabravo	CAN can use any kind of wire you like. It is only if you want to push the limits of the technology that special purpose cabling is used. In the special purpose network cables used for CAN, the cables are characterized and the values are consistent from one spool to the next. __________________ We never have time to do it right; but we always have time to do it over. Last edited by Papabravo; 3rd November 2009 at 01:55 PM.

3rd November 2009, 06:40 AM	#3
Oznog	CANbus is by definition a differential pair, essentially two wires plus ground. They generally need to be a twisted pair. Assuming this is PIC, the PIC's CANbus implementation requires a simple CAN transceiver chip. You might think you can take the CAN Tx out of one PIC and feed it into the CAN Rx of another chip and vice versa, but no, that's impossible. Unlike the UART, the CAN protocol will not support this type of connection. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes. Last edited by Oznog; 3rd November 2009 at 06:41 AM.

3rd November 2009, 11:48 AM	#4
Sathiesh Kumar	Then how the connections has to be made between two nodes...

3rd November 2009, 08:33 PM	#6
Oznog	What are you trying to connect? A PIC with a CANbus port, or CAN controllers, or what? __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

3rd November 2009, 09:00 PM	#7
NHN	I've used some basic .35-.5mm electrical wiring for canbus in my car mate, cat5 stranded network wiring will do I should think no?

4th November 2009, 04:16 AM	#9
Oznog	CANbus should be wired in a line, with no "star" branch connections. And the ends must be terminated with a specified resistance to avoid causing reflections back down the bus. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

4th November 2009, 07:18 AM	#11
Oznog	I'm just going by what is stated in the CANbus specification. I do distinctly recall that branches were a no-no (but that's not saying it'll always be a problem), and that the end of the string needed termination. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

4th November 2009, 07:29 AM	#12
atferrari	In real circuits I hade the chance to see, short stubs are common. I personally understand that "adding" nodes would be impractical if the "line" should be extended for every newcomer to the already working circuit. I admit my lack of practical experience other than having worked out a running CAN network with three PICs on my bench. __________________ Agustín Tomás In theory, there is no difference between theory and practice. In practice, however, there is.