SN65DSI86: Questions for the IRQ pin define

Part Number: SN65DSI86

Hi Expert,

I have some questions about the IRQ pin of SN65DSI86 below. Please help to check it.

1. What the purpose is for the IRQ, i just know that is interrupt signal, no more detail description for this pin function and purpose.
2. If it is not used, how can it do?
3. If it has to be used, what the default setting is? PU or PD?

thanks,

Mark