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Inquiry regarding maximum signaling rates on SN65HVD257

Atsushi Okui
Genius 4015 points
Other Parts Discussed in Thread: SN65HVD257, SN65HVD1040, SN65HVD255, SN65HVDA1040A, SN65HVD256

Hello, all

Now we are considering to use SN65HVD257, then would like to know the detail on the maximum signaling rates on this device.

When referring the datasheet of SN65HVD1040, this rate is defined as 250kbps when the bus length is 250m.

However, on the datasheet of SN65HVD257, same definition could not be found.

We assume that the maximum signaling rates itself on SN65HVD257 is higher than SN65HVD1040. Then we need to clarify this rate.

Actually, we need more than 250kbps when the cable length is 300m.

We thank you in advance for your information. 

Best regards, 

  • 0
    TI__Mastermind 21336 points

    Hi Okui-san,

    There will be a trade-off between the maximum length of the bus you can have, and how many nodes you place on the bus in conjunction with protection components.

    All transceivers, bus capacitors, transient protectors and cabling contribute to the total amount of capacitance on the bus.. This will in turn limit the maximum speed that you can operate at.

    If you can tell me more about your system, how many nodes, if you plan to have external protection, the type of cabling you will be using, I can try to help you estimate the maximum speed you will be able to operate at.

    Thanks,

    John

  • 0 in reply to John Griffith
    TI__Mastermind 21336 points

    Okui-san,

    Also I noticed you are looking at the SN65HVD257 and were comparing it to the SN65HVDA1040A. Are you looking for a redundant CAN network? If not, you might be better looking at the SN65HVD255 or 256 which are in the same Turbo CAN family with our latest CAN driver technology.

    Some higher layer protocols have standardized the following guidelines, 1MBPS @ 40m, and 125KBPS @ 500M. Our new Turbo CAN devices will be able to better depending on the network you are using.

    Thanks,

    John

  • 0 in reply to John Griffith
    Genius 4015 points

    Griffith-san,

    Thank you for your reply on this inquiry.

    I could get some detailed information regarding their system.

    - Maximum number of nodes: 30

    - External protection

    => Common mode filter "ZJYS81R5-2P24-G01" is used on CAN line. Please refer to the website below for the detail of this filter.

    http://www.tdk.co.jp/etvcl/equivalent/data/cmf/zjys81.pdf

    Also, the cable type they are using is TTYCS, which contains twisted pair cable, vinyl isolation, Vinyl sheath, Wickerwork decoration and shield. 

    We thank you once again for your information.

    Best regards,

  • 0 in reply to Atsushi Okui
    TI__Mastermind 21336 points

    Hi Okui-san,

    There are a couple of application notes that I have read on this topic, and I wanted to share them with you. I am concerned that the system you are descibing may not work, but if it does, there wil not be much margin left for noise, varying power supply voltage, and other system level paramters.  

    The first application note I wanted to share is from CANopen and it has a table on page 6. You can see from this table that as the cable lengthes get longer, better cabling is required. They state that you can acheive 500KBPS at 100 meters and 100KBPS at 500 meters. So based on this table you are on the border of there recommended max speed.

    4505.CANopen_Cabling.pdf

    The second table I wanted to share which has a link to it below, was written by CAN in Automation (CiA). They published a table that has bit rate vs. bus length. It is recomending that you operate a network with length of 250 meters no faster than 250KBPS. So for 300 meter you would have to go slightly slower by their recomendation.

    http://www.can-cia.org/index.php?id=158

    The newer TI devices that we call our Turbo CAN devices will be capable of faster data-rates with longer bus lenthes. These devices include SN65HVD255, SN65HVD256 and SN65HVD257. And like I said befroe, a better regulated power supply, better cabling will also allow the system to operate at slightly higher datarates.

    Thanks,

    John