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ISO3086T: Low speed drive

Kenji Ohno1
Genius 5095 points
Part Number: ISO3086T

Hi Team,

This is a product with a specification upper limit of 50 Mbps. Is there a problem with using at low speed?

My customer wants to use at 9.6 kbps.

This device recognizes that it has not lined up for low speed.

Please let me know if there are points to be careful when using at low speed

I found the following.

https://e2e.ti.com/blogs_/b/analogwire/archive/2019/04/09/frequently-asked-questions-and-answers-for-rs-485-transceivers?jktype=e2e_blog

”the lower-frequency range, where the interaction between the cable series resistance and the end-of-line termination results in attenuation of the signal. ”

If there is a possibility that V IT threshold will not be exceeded, what measures should be taken?

Best Regards,

Kenji

  • 0
    Guru 243910 points

    Section 8.4 of the datasheet does not show any timeout; there is no lower speed limit.

    The linked blog post talks about effects that happen in extremely long cables, where the resistance of the cable conductor becomes too high. Are you using 1 km cables? If yes, you can reduce the cable resistance by using wires with a larger diameter, or using multiple wires in parallel.

  • 0 in reply to Clemens Ladisch
    TI__Genius 17100 points

    Thanks for your response, Clemens!

    Kenji,

    As Clemens mentioned, there is not a lower speed limit for RS-485 or for the ISO3086T specifically, but depending on cable length, it has a maximum limit of 20Mbps*. 9600 bps is common for low-speed and long distance applications, and there are not many considerations to keep if  wires/cables are short and there are few nodes on the bus. For optimal signal integrity, it is always best to match the AC line impedance with a termination of equal value, however termination networks are not critical in systems where two-way loop time of the network is much greater than a single bit time (~<0.1×two-way loop delay) as explained in this blog post.

    For methods to calculate how many nodes can be connected to a bus, please check out this FAQ.


    Thank you for posting to E2E! Feel free to reply if you have additional questions or would like more information.


    Respectfully,
    Manuel Chavez

    *PSA: To clarify the original post, ISO3086T has a maximum signaling rate of 20Mbps

  • 0 in reply to Manuel Chavez
    Genius 5095 points

    Hi,

    Thank you for your answer.

    I understood well.

    Best Regards,

    Kenji