DFR0259 RS485 Shield - RS485-B signal it's not working properly

I tested NUCLEO board + DFR0259(RS485 Shield) for RS485 communication test,

but it seems that RS485-B signal is not working properly.

In my opinion, RS485-B(Expansion) should be “LOW” state before the data is transmitted, however, when I measured the signal with a logic analyzer, the signal was in a "HIGH" state before the data was transmitted. Am I right?

If yes, how can I change this state for RS485-B expansion?

As I searched, it can be changed only hardware adjustments… then, is this issue because my DFR0259 is a defective product?

I'd sincerely like to solve this problem…

If you have any good idea or find my mistake, please feel free to let me know!

Thank you!

<Pre-conditions>

Baudrate: 115200

Word length: 8bits(9bits including parity)

Parity: Even

Stop bits: 1