Figure $1\mathrm{.}6$: RS $485$

For RS$-485$ part, we use an IC MAX$485$ to convert UART signal to $485$ signal and vice versa.

We also use a RJ$45$x$2$ to connect RS$-485$ signals. Last thing we need to consider for this part

is that RJ$45$ xx$2$ is also supply $5$ V input, so we use D $1$ to prevent the current go through the

RS$485\_5$V pins.

Question: What is the main purpose of D$2$ in the given figure. And explain how this circuit work.

Thank you so much