8085MICROPROCESSOR ARCHITECTURE

In the commons  language  the architecture means  structural  design of  a building. Similarly by microprocessor  architecture in  a broad sense we mean the structural design of the digital circuit responsible  for computing. The digital circuit of the microprocessor is designed in such a way that if  a proper binary input called  instruction) is given  to this circuit  we get the desired output. To understand this we can see the behaviour of a two input  AND  gate in which  we get 1  as an  output if and only if both the input are 1 similarly  an adder circuit gives  the output which is the addition of two input bits. Hence we can imagine that how  complicated is the design of the digital circuit of an microprocessor which  can give  the output according to various instruction given to it like add subtract move  and or exclusive or etc. This can be  achieved in  different  manner. That means there may be many possible digital circuits to achieve in different manner. That means  there may  be many possible  digital circuits to achieve the same output. Therefore the architecture of two different microprocessors might be different. The  way they ad two numbers may be quit similar but a complicated task like finding out the tangent of an  angle will be performed in a different way in two  different microprocessors. One microprocessor may perform it very easily while the other may with difficulty.

Various   features  which  affects  the architecture of  a microprocessor are:

a.Length  of data word  which is decided by the size of the data bus.

b.The size of  memory  accessed by  the microprocessor which is  decided by the size of the address bus.

c.The  speed  of execution  of instruction which  id seceded by the  clock  frequency at  which  microprocessor  can  operate.

d.The type of registers.

e.The types  of instructions.

f.The types  of addressing  modes.

g.Various  supporting hardware  which are compatible  with that  microprocessor.

These are  various features which  make are  microprocessor different from  other microprocessor. We will discuss these features in detail in different parts of this book  especially for 8085 microprocessor. Various  advanced processors  are discussed in chapter 11.