Modbus RTU over RS485 slave library for Nano

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I think that this is an original Arduino Ethernet Shield R3

IMG_20211102_071155
IMG_20211102_0711551530×2040 371 KB

I power both of Arduino Nano and the Ethernet Shield with USB from my laptop.

Also tried to connect the TX and RX pins, but with no success. The Ethernet Shield still couldn't be found.