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ISOW1412: tpZH / tpZL

Shuji Ishiwata
Mastermind 8880 points

Part Number: ISOW1412

Hi All,

I have a question about the ISOW1412.
After RE is set low, data is output from the R terminal 640 usec later.
As a result, the data is not being received correctly by the MCU.

image.png

According to the datasheet, tpZH and tpZL have a maximum of 30 nsec.
Why is the data output 640 usec later?

If the device communicating via 485 adds a wait time (about 50 usec) when sending data, reception will be successful.


Best Regards,
Ishiwata

  • 0
    TI__Genius 16050 points

    Hello Ishiwata,

    Thanks for reaching out and providing clear details of the issue.

    The Output of R will also be dependent on A/B levels on RS485 bus side. Do you have the waveforms for A and B while keeping the above sequencing same as shown in the waveforms above?

    We want to see the RE, R and A,B waveforms together keeping all the signal sequence same.

    Also please understand the expected delay will not only be based on "Receive Enable" time but also the "Driver Disable time" hence it cannot be 30ns.

    Regards
    Varun

  • 0 in reply to Varun Kumar
    Mastermind 8880 points

    Hi Varun,

    Thank you for your support.
    Below are the waveforms for RE, R and A,B.

    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Genius 16050 points

    Hello Ishiwata,

    Thanks for the inputs.

    As per these waveforms it can be clearly seen that the R pin is behaving as expected.

    After RE is pulled low, there is a 640us LOW(VB>VA) on RS485 bus which is what gets reflected on R as well.

    As soon as VA>VB -> R also follows the same.

    You need to Investigate the Bus side connected device for the 640us duration of VB>VA since that is what is causing the delay here and not ISOW1412 enable/disable time.

    Regards
    Varun