Microprocessor based System Block Diagram

Basic Functional Blocks of a Microprocessor 

Register Array:

Register array is group of registers. Register array contains general purpose registers and special purpose registers. It is used for temporary storage of data.

Instruction Decoding Unit:

Instruction decoding unit decodes the instruction. In order to execute (perform) the operation, all data should be decoded. The processor cannot perform the execution, if data are not decoded.


All the arithmetic and logic operations are performed with respect to ALU. The execution is taken inside the ALU.

Timing and Control Unit:

In order to perform all the operations, some predefined timing period is required. That is, with respect to the time period, the processor will works. The control unit releases the control signal. Control Signal provides control to both the processor and to the peripheral devices.

Flag Register:

Flag register is very near to ALU. “Flag register keeps the status of the last operation”. That is, by the help of flag register, the processor can understand the status of the last operation. Processor cannot access the data directly from the flag register.

In 8086 Processor, all the general purpose and special purpose registers except deoding registers are 16 bit registers.

Program Counter (PC)/ Instruction Pointer (IP):

Instruction pointer will store the address of the next instruction to be executed. That is, the address of the next instruction to be executed is stored in PC.

In 8086, PC is a 16 bit register. This means that, in 8086, 20 address lines are used. So the 8086 has 16-bit registers and 20 address lines.

In 8085 Processor, 8 bit registers and 16 number of address lines are used.

Total Memory that can be accessed by any processor = 2number of address lines.

In 8085 Processor, Total Memory that can be accessed = 216 bytes = 64 KB

In 8086 Processor, Total Memory that can be accessed = 220 bytes = 1 MB

Note: In 8086 processor, each memory   can save only 8 bit data. So in order to store 16-bit data, two consecutive memory locations are needed. 8086 Processor is a 40 Pin Processor.
Memories are classified into

(a) Even Memory
(b) Odd Memory

Microprocessor based System:

Microprocessor based System Block Diagram is shown below.

In order to perform every operation, the processor should require some peripheral (supporting) devices such as memory, input base, output base etc. Microprocessor is a parallel communicating device.

8086 processor works under a set of instructions.

RAM – used for Read and Write Operations
EPROM – Erasable Programmable ROM

In a processor, Data and control bus are bidirectional, but address bus is unidirectional.

In 8086 processor, 16 address lines and 20 data lines are Multiplexers. At other times, it acts as data bus. In 8086 processor, first 16 data lines are multiplexed with first 16 address lines. A multiplexer cannot perform any operation directly.

Sreejith Hrishikesan

Sreejith Hrishikesan is a ME post graduate and has been worked as an Assistant Professor in Electronics Department in KMP College of Engineering, Ernakulam. For Assignments and Projects, Whatsapp on 8289838099.

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