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ISO7721: Related to UART Connection

Kim Hyerin
Prodigy 10 points
Part Number: ISO7721


Tool/software:

Dear Team.

I'm using ISO7721DR and MAX13488 for RS485 communication.
Attached is the circuit diagram.

I checked that it is working, but there's a strange thing. As far as I understand, ISO7721 insulates what comes in as input and sends it out as output.

Then, according to my circuit, the TX of the CPU comes out, passes through ISO7721, goes into D of MAX13488. and the RX of the CPU goes through ISO7721 into R, right?

But it's weird that UART's RX and TX communicate without intersecting.

Isn't there a separate function that intersects inside ISO7721?

Best Regard,

Hyerin

  • 0
    Guru 318700 points

    The A and B channels are completely independent.

    TX does not affect RX because the MAX13488's RO pin is disabled while it is transmitting.

  • 0
    TI__Mastermind 18885 points

    Hi Hyerin,

    Thanks for reaching out.

    Kim Hyerin said:
    Then, according to my circuit, the TX of the CPU comes out, passes through ISO7721, goes into D of MAX13488. and the RX of the CPU goes through ISO7721 into R, right?

    Yes, that is correct.

    As Clemens pointed out, Channels A and B are both independent from each other. This means that TX and RX of the isolator are completely independent. 

    Kim Hyerin said:

    But it's weird that UART's RX and TX communicate without intersecting.

    Isn't there a separate function that intersects inside ISO7721?

    I'm not completely sure what you mean by "intersecting", but you can think of the isolator channels as a "buffer", where the signal simply passes from the primary circuit to the secondary circuit. Therefore, the TX does not affect the RX or vice versa. 

    Regards,
    Aaditya Vittal