to study internal architecture of any processor u should know the concepts of computer organisation. go for morris mano. u will gwt details of internals of processor
actually any microprocessor is like mind of human being and is in still development. so to understand the microprocessor we also hav to understand the functions and work a microprocessor can do. so in that way its not a single line answer. u hav to understand the architecture, memory management, peripheral interfacing by 8085 to understand the actual concept of 8085.
RAMESH GAONKAR is a nice book if u want to get the fundamentals of 8085. it really covers most of the concepts of 8085.