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What is the reason why the 485 circuit does not communicate?

Hardware design
juillet 03, 2020 by Margo 1359

This is the 485 circuit I designed.


After the power is turned on, the D/R pin is always high regardless of whether the MCU_D/R pin outputs a high level or a low level. What is the reason?

485电路

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Yuri Posté sur July 3, 2020

That's the problem of optocouplers. For the next 8.5CA, it is better to use 12CA.

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  • Lars

    Lars Posté sur July 3, 2020

    I changed the TTL end resistor 511 to 101, 485 end pull-up resistor, 102 to 103

    , But this is not suitable for long-term operation of the microcontroller.

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Janna Posté sur July 3, 2020

The drive current is small and the optocoupler is not fully turned on, resulting in no change in level.

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