在进行端子定义设定的过程中注意到端口属性中有DSIS这一条，式样书中相关描述如下：
- DSIS: The deselected input state (DSIS) indicates the state driven on the peripheral input (logic "0", logic "1", or "PIN" level) when the peripheral pin function is not selected by any of the PINCNTLx registers.
- 0: Logic 0 driven on the input signal port of the peripheral.
- 1: Logic 1 driven on the input signal port of the peripheral.
• An empty box means Not Applicable.
关于这一条属性应该怎么理解呢？
描述中提到的PINCNTLx寄存器也没有在式样书中找到对应功能，请问使用做什么呢