Re: CAN bit timing, Seg2 =1Tq

Hello,

125ns from the end of the bit means 87.5%, which is far end of the standard SP location in 1Mbps CANopen. So, there should not exist any problems with that. But, please note that the earliest SP location is still 75%, meaning that there may exist other devices using such! So, you can only have 4TQ (=500ns) for signal propagation, from which transceivers take approximately half. There shall always exist at least 1TQ phase segment 1 enabling non-zero SJW. That means that after subtracting transceiver delays, you'll anyway have 250ns left for back-to-back propagation in the network cabling, resulting 25m maximum achievable network length (25m*2*5ns/m=250ns).

800kbps may be selected, but there is a practical drawback -- there are too many devices not supporting it. So, it is recommended to search 2-3 2nd source devices as a background. If such do not exist, one option may be the use of switch, which receives and re-transmits the frames and thus doubles the maximum achievable segment length.

Best regards,

-H

Heikki Saha, CTO
  M.Sc. Automation
  Dr.Tech. Electronics
TK Engineering Oy
Mail address:  P.O. box 810, FIN-65101 VAASA
Visit address: Yrittäjänkatu 17, FIN-65380 VAASA
+358 (0)50 588 6894
email: [email protected]
skype: heikki.saha_tke
http://www.tke.fi/
http://www.canopen.fi/

----- Original Message -----
From: "Bertil Bäck" <[email protected]>
To: [email protected]
Sent: Thursday, September 1, 2016 3:06:12 PM
Subject: Re: [CANLIST] CAN bit timing, Seg2 =1Tq


CANopen also specifies 800kbps as speed. If you don't want to drop down to 500kbps. 

Depending on what you do you can also run other speeds. 

Br, 
Bertil 

----- Original Message -----

From: "Amitai Broyde" <[email protected]> 
To: [email protected] 
Sent: Saturday, July 16, 2016 5:01:57 PM 
Subject: Re: [CANLIST] CAN bit timing, Seg2 =1Tq 




Got it, 

Thanks, 



ab 



‫בתאריך שבת, 16 ביולי 2016 ב-15:05 מאת ‪Bram Kerkhof‬‏ <‪ [email protected] ‬‏>:‬ 






The first thing I usually do in these kinds of situation is rethink whether I am: 

A) Using the right technology 

B) Using the technology right 



The big advantages of CAN for me are that it is cheap, simple and reliable as long as you keep away from the bleeding edge (it’s called ‘bleeding’ for a reason ;-). 

When pushing the limits like this, you’ll end up with a system that’s either cheap and simple or reliable, which is probably not what you want. 



Keep in mind that impedance is everything at this point, and that you don’t only have to consider the backbone cable, but also all the connections in between. What works for 35m between two nodes, may not work over the same distance with multiple nodes on the bus. 



Do you really need 1 mbits? Chances are you can simply drop down to 500kbits without too much work. 

If throughput is an issue, consider splitting the network with a gateway. If timing determinability is an issue, consider a time-sensitive protocol implementation (like TTCAN) and a lower bandwidth. 



Or use something else entirely. 



Cheers, 

Bram 



From: [email protected] [mailto: [email protected] ] On Behalf Of Amitai Broyde 
Sent: vrijdag 15 juli 2016 9:30 
To: [email protected] 
Subject: [CANLIST] CAN bit timing, Seg2 =1Tq 







Hi, 


I am using 1Mbps CAN network based on Cores running at 8MHz. I would like to extend the bus length by setting sampling point 125ns before end of bit time. Current bit sampling time is 250ns before end of bit time. 


Will it work? 





Regards, 


ab 
--
Archives and useful links: http://groups.yahoo.com/group/CANbus
Subscribe and unsubscribe at www.vector.com/canlist/
Report any problems to <[email protected]>