How do you interface 8085 microprocessor?

Interfacing 8085 means the way to properly connect the microprocessor with the outside unit i.e. I/O unit and the inside unit i.e. Memory unit. So, there are two types of interfacing: I/O interfacing and Memory interfacing.

I/O interfacing means how to connect MP to the peripheral devices e.g. 8255A, 8251A etc.

Memory interfacing means how to connect MP to the memory devices e.g. RAM, ROM, EPROM etc.

For the interfacing, the remaining address pins must be decoded using the technique called "Address Decoding". This technique uses following decoders to decode:

i) Logic Gate Decoder (Simple NAND Gate decoder)

ii) Line Decoder

      - The 1-to-2 line decoder

      - The dual 2-to-4 line decoder

      - The 3-to-8 line decoder

8085 microprocessor has 16-bit address i.e. it uses 16 pins for address bus. Suppose, we have to interface with 4 KB RAM. This RAM has 12-bit address bus (2^12=4*1024 bytes). Lower 12-bits (A0-A11) of MP gets directly coonected to address pins of RAM. But, what about other upper 4-bits  (A12-A15) address of MP. These pins are the things needed to be decoded by using above decoders. 

Fig; memory interfacing using NAND gate decoder

Fig; memory interfacing using 3*8 decoder