Disign GPIB interface using NAT9914+stm32F103 microcontroler

hi,

    I am design a GPIB interface board based on the NAT9914 and stm32F103 microcontroler,but I don't know how to read/write the registers,can you give me an example?such as provide me two functions Output(U8 add,uint data);Input(U8 Addr); I have read some document ,but I don't know what's the Addr means,please see the photo bellow,I use PORTD to read/write the registers,what is the address of register relate to the microcontroler? thank you!