Re: can network establishing -- Can bit timing

Heikki
your answer is well done. Can I add it to
http://www.can-wiki.info/doku.php?id=can_cabling

Or better, ask for a login and add what ever you like, it's a wiki.
 
 Heinz

Am Freitag, 18. Oktober 2013, 13:48:32 schrieben Sie:
> Hello Eric,
> 
> Propagation delay consists of:
> - Propagation delays of transceiver: TX-to-CAN _and_ CAN-to-RX
> - Propagation delay of logic, if additional logic exist between controller and transceiver
> - Propagation delays of isolation, if such is used
> - Signal propagation delay required for signal to go from end to end of the network _and_
>   back. Propagation delay needs to be taken as twice, because during arbitration and ACK,
>   network state may be driven by multiple devices and there shall be enough time to enable
>   network state to stabilize before taking a sample.
> 
> Some example values:
> - TJA1050: TX-to-CAN worst case 110ns, CAN-to-RX worst case 155ns
> - Logic depends on the implementation, but fast CPLDs such as Lattice ispM4A provide <10ns
> - Best option is to use digital isolators, e.g. for ADuM1100 worst-case 18ns
> - Signal propagation delay is 5ns/m in standard 120ohm CAN-cable
> 
> => Basic implementation without isolation and logic, we get:
>    1: At 1Mbps CANopen we have 4TQ=500ns reserved for propagation delay in a worst case
>    2: 110ns + 155ns = 255ns for transceiver -- 195ns is left for signal propagation
>    3: We can achieve maximum cable length of 195ns/(2*5ns/m)=19.5m
> 
>    4: If we have the best possible 5TQ=625ns propagation segment
>    5: Maximum cable length of 320ns/(2*5ns/m)=32m may be achieved
> 
> => The basic timing is only one part of the truth. Additional constraints are required for
>    the topology to keep the transmission line solid:
>    - Few group of devices far away from each other should be avoided, because the groups
>      modify the line-impedance in the area of the group => impedance junctions introduce
>      reflections
>    - In addition to previous, residual error probability decreases significantly when the
>      number of devices are increased -- use numerous devices, but try to install them evenly
>      along the network.
>    - Too long drop-lines are unterminated ends, causing reflections => the longer drop-line,
>      the closer to sample point the reflection can appear. The more there are long drop-lines,
>      the higher power reflections appear
> 
> That was timing in brief. I hope you got some help.
> 
> Best regards,
> 
> -H
> 
> 
> TK Engineering Oy
> Heikki Saha, CTO
>   M.Sc. Automation
>   Dr.Tech. Electronics
> Mail address:  P.O. box 810, FIN-65101 VAASA
> Visit address: Yrittäjänkatu 15, FIN-65380 VAASA
> +358 (0)50 588 6894
> [email protected]
> http://www.tke.fi/
> http://www.canopen.fi/
> 
> ----- Original Message -----
> From: "Eric clawson" <[email protected]>
> To: [email protected]
> Sent: Friday, October 18, 2013 1:21:57 PM
> Subject: Re: [CANLIST] can network establishing -- Can bit timing
> 
>

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