This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ISOW1412: Application circuit for Full-Duplex and Half-Duplex

Part Number: ISOW1412

Hi Sir,

May I know the figure 11.3 of the datasheet, is it a full-duplex configuration? if it is, why the DE/RE are shorted to each other?

another question is this user guide "Optimize Your Design with Isolated RS-485 Transceivers with Integrated Power", the figure 2 of the document, is it a half-duplex configuration? if it is, why the DE/RE are not shorted to each other?

  • Hi Henry,

    Thanks for reaching out.

    The shorting of DE/RE in Figure 11-3 of ISOW1412 datasheet is a incorrect for full-duplex operation. They need to be controlled separately to operate the system in full-duplex, apologies for this error in the datasheet and thanks for letting us know. We will try to get this fixed in our next revision of datasheet.

    Figure 2 in the applications brief document (SLLU334) that you referred is configured for half-duplex. It is a common practice to short DE/RE together for half-duplex operation but it is not mandatory. They can still be controlled separately and still operate in half-duplex without any issues. Hence, this connection is not a problem although is not a common practice. I will also reach out to the author to see if they would like it to stay as is or want it changed. Either ways, it is going to be correct.

    Let me know if you have any questions, thanks.


    Regards,
    Koteshwar Rao

  • Hi Sir,

    My customer would like to know the document (SLLU334), what is the function of output resistor at port A/B?

    The EVM user guide document (SLLU324A), why use the different configurations on the A/B and Y/Z? A/B for full-duplex? Y/Z for half-duplex?

  • Hi Henry,

    Thanks for further inputs.

    My customer would like to know the document (SLLU334), what is the function of output resistor at port A/B?

    The series resistors (usually 10Ω) on A/B or Y/Z pins are to limit current into the device bus pins when a transient is applied. The TVS diode does protect the bus pins by clamping voltage while these resistors provide additional protection by limiting the current into device pins. These are not required for normal operations but are useful for protection against EMI transients.

    The EVM user guide document (SLLU324A), why use the different configurations on the A/B and Y/Z? A/B for full-duplex? Y/Z for half-duplex?

    I believe you are referring to the implementation of termination resistor on A/B and Y/Z bus pins being different. The schematic demonstrates two kinds of terminations, one is just a simple termination using one 120Ω resistor between A/B lines while Y/Z pins demonstrate termination resistors with differential filtering by using two 60Ω resistors with a filtering capacitor connected to their mid-point.

    Either of these terminations can be used for either of the bus pins. Use differential terminations for all for better noise filtering. I hope this clarifies your question, thanks.


    Regards,
    Koteshwar Rao