Internal Architecture of 8085 Microprocessor Notes
This is the block diagram of internal architecture of 8085 microprocessor. In this post brainstocker.com is going to throw some light on the Intel 8085. We are going to provide you with the brief notes on 8085 microprocessor.
Introduction to Internal architecture of 8085 microprocessor:
Intel 8085 microprocessor is a 8- bit microprocessor. It is a 40 pins IC packets fabricated on single large scale integrated chip. Intel 8085 uses single +5V DC supply. Its clock speed is about 3 MHz. It has 80 basic instructions and 246 opcodes (operational codes).
It consists of following three main sections:
- Arithmetic Logic Unit.
- Control Unit and set of register.
- Timing and control circuit.
Brief explanation of internal architecture of 8085 microprocessor
Arithmetic Logical Unit (ALU):
ALU performs arithmetic and logical operations such as addition, subtraction, multiplication and logical AND, logical OR, increment, decrement, left shift, right shift, rotate left and rotate right.
These are some of the logical and arithmetic operations that are performed by ALU.
Timing and control circuit:
It is the section of CPU. It generates timing and control signal which are necessary for the execution of instructions. It controls data flow between CPU and peripheral devices. It provides status control and timing signals which are required for the operations of memory and I/O devices.
Control unit and Set of registers:
Registers: Registers are used by microprocessor for temporary storage and manipulation of data and instructions. Data remains in registers till they are sent to the memory or I/O devices. Intel 8085 microprocessor has following registers.
- One 8- bit accumulator register
- Six 8- bit general purpose registers
- One 16- bit stack pointer
- One 16- bit program counter
- Instruction Register
- Temporary Register
8- bit Accumulator: The accumulator is 8 bit register associated with ALU. It is used to hold one of the operand of an arithmetic or logical operations. It serves as one input to the ALU. The operand for arithmetic or logical operation may be stored either in the memory or in one of the general purpose register. The final result of an arithmetic and logical operation is placed in the accumulator.
General Purpose Registers: The 8085 microprocessor contains 6 general purpose registers. They are B, C, D, E, H and L to hold 16 bit data. The combination of two 8- bit register is used for storage. These are known as register pairs. The valid combination of register pairs of 8085 are BC, DE and HL. The HL pair is used to act as memory pointer and for this purpose it hold 16- bit address of a memory location.
Program Counter: It is a 16- bit special purpose register used to hold the address of next instruction to be executed. It keeps track of memory location or address of the instruction in a program while they are being executed. The microprocessor increment the content of the program counter during the execution of an instruction in the program at at the end of the execution of the instruction.
Stack Pointer: It is a 16- bit special purpose register. The stack is a sequence of memory location set aside by programmer to store or retrieve the contents of accumulator, flag, program counter and general purpose registers during the execution of the program. Since Stack works of LIFO principle it operates faster than normal store and retrieve of memory location. The stack is defined and the stack pointer is initialize by the programmer at the beginning of the program which needs stack operations.
Instruction Register: The instruction register holds the operational code or instruction code of the instruction which is being decoded and executed.
Temporary register: It is a 8- bit register associated with ALU. It holds the data during arithmetic or logical operation.
Flags: Intel 8085 microprocessor contains 5 flip flops to serve as flag. The flip flops are set or reset according to conditions which arises during an arithmetic or logical operation. The five flags are as follows:
- Carry flag
- Parity flag
- Auxiliary carry flag
- Zero flag
- Sign flag
Data and Address Bus: 8085 has 8- bit data bus and 16- bit address data bus. The MSB of the address are transmitted by address bus and LSB of address is transmitted by address/ data bus.