Architecture of 8085 – Functions of Each Block | New Topic [2024]

In this note, we are going to learn about the Architecture of 8085, and functions of each and every block of this architecture of 8085. Welcome to Poly Notes Hub, a leading destination for Engineering Notes syllabus wise.

Author Name: Arun Paul.

What is 8085 Microprocessor?

The Architecture of 8085 Microprocessor is based on an 8-bit data bus and 16-bit address bus. It has a simple instruction set and is well-suited for basic computing tasks and control applications.

The Intel 8085 is an 8-bit microprocessor that was introduced in the mid-1970s. It played a significant role in the early development of microcomputers. The architecture of the 8085 can be divided into different components.

It has the following specifications:

1. 8 Bit Data Bus.
2. 16 Bit Address Bus
3. Address bus can be address upto 64 kB
4. A 16 bit SP ( Stack Pointer )
5. 16 bit PC ( Program Counter )
6. Required +5V supply.
7. Much slower in operation, compare to 8086 Microprocessor.

Applications of 8085 Microprocessor:

1. The 8085 microprocessor is commonly used in embedded systems to operate a variety of devices and appliances. Its low power consumption and simple construction make it ideal for industrial automation, home automation, and automobile systems.
2. In some medical equipment, such as patient monitoring systems, the 8085 microprocessor is used to control and interpret sensor data, display information to medical personnel, and conduct simple computations.
3. Because of its low cost and dependability, the 8085 microprocessor may be used for control and user interface functions in some older types of home appliances like as microwave ovens, washing machines, and air conditioning units.

Internal Architecture of 8085 Microprocessor

This is the Architecture of 8085 Microprocessor with many sections. Each section has it’s own function and task by which the whole architecture of 8085 microprocessor works.

Functions of Each Block

Below we discuss the function of each and every section of the architecture of 8085 microprocessor.

• Timing and Control: The “Brain” of the microprocessor is represented by this box titled “Timing and Control“. This is the sequential machine that we have talked about earlier. Note that the input to the timing and control logic comes from the next “Instruction” of the currently running program.
• ALU and Flags: The ALU is the component of the Microprocessor that carries out the Arithmetic (like add, subtract, div etc.) and logical (like AND, OR etc.) on two input operands and produces and output. Connected to the ALU, there is a set of five flags. These flags are-
  1. Z or Zero Flag: SET when the result of last operation leaves all zeroes.
  2. S or Sign Flag: SET when the last operation makes bit-7 (i.e. the most significant bit) of the result 1.
  3. P or Parity Flag: SET when the last operation leaves an even number of 1-s in the result.
  4. C or Carry Flag: SET when the last arithmetic operation involves a carry or borrow out of the MSB.
  5. AC or Auxiliary Carry Flag: The 8085’s Auxiliary Carry (AC) flag indicates carries that range from low to high levels.

Below we listed some flags with their status:

• Register Bank: There are seven internal 8-bit registers that can be referred to by instructions. They are called B, C, D, E, H, L, and A. The A register is actually the Accumulator that we have talked about in the discussion on ALU.
• Accumulator: It is an 8-bit register used to perform arithmetic, logical, I/O & LOAD/STORE operations. It is connected to internal data bus and ALU.
• Temporary Register: It is an 8-bit register, which holds the temporary data of Arithmetic and Logical Operation.
• Instruction Register and Decoder: It is an 8-bit register. When an instruction is fetched from memory then it is stored in the instruction register and the work of instruction decoder to decode the instruction.
• Stack Pointer: In 8085, the stack pointer is a 16 bit register that is used to point into memory representing the stack.
• Program Counter: In 8085, the Program Counter is maintained as a 16-bit internal register. Under ‘Normal Control Flow’, the program counter is increments after every byte of the next instruction in ‘fetched’.