__ARCHITECHTURE or FUNCTIONAL BLOCK DIAGRAM OF 8085__

**The functional block diagram or architechture of 8085 Microprocessor is very important as it gives the complete details about a Microprocessor. Fig. shows the Block diagram of a Microprocessor.**

**Accumulator (A):**

**The accumulator is an 8-bit register that is part of the arithmetic/logic unit (ALU). **
**This register is used to store 8-bit data and to perform arithmetic and logical operations. **
**The result of an operation is stored in the accumulator. **

**Flags:**

**The ALU includes five flip-flops that are set or reset according to the result of an operation. **
**The microprocessor uses the flags for testing the data conditions. **
**They are Zero (Z), Carry (CY), Sign (S), Parity (P), and Auxiliary Carry (AC) flags. The most commonly used flags are Sign, Zero, and Carry.**

** The bit position for the flags in flag register is,**

**1.Sign Flag (S): **

** ****After execution of any arithmetic and logical operation, if D7 of the result is 1, the sign **** **** ****flag is set. Otherwise it is reset. **

** ****D7 is reserved for indicating the sign; the remaining is the magnitude of number.**

** ****If D7 is 1, the number will be viewed as negative number. If D7 is 0, the number will be **** **** ****viewed as positive number.**

**2.Zero Flag (z): **

** ****If the result of arithmetic and logical operation is zero, then zero flag is set otherwise it is reset.**

**3.Auxiliary Carry Flag (AC): **

** ****If D3 generates any carry when doing any arithmetic and logical operation, this flag is set.**

** ****Otherwise it is reset.**

**4.Parity Flag (P): **

** ****If the result of arithmetic and logical operation contains even number of 1's then this flag will be **** ****set and if it is odd number of 1's it will be reset.**

**5.Carry Flag (CY): **

** ****If any arithmetic and logical operation result any carry then carry flag is set otherwise it is **** **** ****reset.**