8085 Architecture

Arithmetic Logic Unit

The ALU performs the actual numerical and logic operation such as ‘add’, ‘subtract’,
‘AND’, ‘OR’, etc. Uses data from memory and from Accumulator to perform
arithmetic. Always stores result of operation in Accumulator.

Control Unit

Generates signals within uP to carry out the instruction, which has been decoded. In
reality causes certain connections between blocks of the uP to be opened or closed, so
that data goes where it is required, and so that ALU operations occur.


Registers
The 8085/8080A-programming model includes six registers, one accumulator, and
one flag register, as shown in Figure. In addition, it has two 16-bit registers: the

stackpointer and the program counter.

They are described briefly as follows.
The 8085/8080A has six general-purpose registers to store 8-bit data; these are
identified as B,C,D,E,H, and L as shown in the figure. They can be combined as
register pairs - BC, DE, and HL - to perform some 16-bit operations. The
programmer can use these registers to store or copy data into the registers by using
data copy instructions.

Accumulator

The accumulator is an 8-bit register that is a part of 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. The accumulator is also identified as register A.