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I am using MAX3362 RS485 serial data transfer IC with ESP32. Marked pins 1, 2 and 3 are connected to GPIOs of ESP32. Do I need to add any additional pull-up resistors or some termination resistors or will this schematic work?

Circuit Diagram

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  • \$\begingroup\$ That will depend what you want to achieve. The pins can be undefined or they may already have pull resistors to some state, and we don't know which pins you have connected them, will ESP32 corrupt the bus when it boots, or will RS485 transceiver prevent ESP32 from booting properly. Also two things may be a problem, you have a fixed termination resistor so you can't put this to an already terminated bus, and you have only two screw terminals for bus, and so you are missing a common bus ground reference terminal. RS-485 is not a two wire bus, it needs two wires and a shared ground. \$\endgroup\$
    – Justme
    Commented Sep 26, 2023 at 17:00

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The RO output is disabled when the /RE is high, so it should have a pull-up resistor. (The internal pull-up of the microcontroller should be enough.)

The receiver does not have failsafe inputs, so the A/B bus lines should have failsafe pull-up/-down resistors (not necessarily on this board, but somewhere on the bus).

A RS-485 bus should have termination resistors only at the two ends, so this board can be connected only to the end of the bus.

All devices on the bus should share their ground, but the connector has only two signals.

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  • \$\begingroup\$ Yes, internal pull-up might be enough. But the pins are floating until software configures them. Unless they are pins pulled low or high with strap resistors to boot into correct mode. \$\endgroup\$
    – Justme
    Commented Sep 26, 2023 at 17:20

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