microprocessor architecture divided in The BIU has to interact with memory and of the programs and to carry out the required processing. EU & BIU. Explanation of the purpose of EU and BIU in Bus Interface Unit (BIU): The BIU interface to outside word. It provides full 16 bit. Define the jobs performed by the BIU and EU in the The functions performed by the Bus interface unit are: The BIU is responsible for the external bus.

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They are dependent and get worked by each other. Below is a short description of these two units. Execution unit receives program instruction codes and data from the BIU, executes them and stores the results in the general registers. This unit, EU, has no connection with the system Buses. It receives microprovessor outputs all its data through BIU.

A register is like a memory location where the exception is that these are denoted by name rather than numbers. All the data, pointer, index and status registers are of 16 bits.

BIU and EU are connected with an internal bus. It is responsible for transmitting data, addresses and control signal on the busses. These all 4 segment registers holds the addresses of instructions and data in memory. These values are used by the processor to access memory locations.

It also contain 1 pointer register IP. IP contains the address of the next instruction to executed by the EU. BIU also contain an instruction queue. When the EU executes instructions, the BIU gets up to 6 bytes of the next instruction and stores them in the instruction queue and this process is called instruction prefetch.


This is a process to speed up the microprocesaor. Also when the EU needs to microproocessor connected with memory or peripherals, BIU suspends instruction prefetch and performs the needed ad.

Execution Unit (EU):

This unit can perform various arithmetic and logical operation, if required, based on the instruction to be executed. Purpose of using Instruction Kicroprocessor BIU contains an instruction queue. A subtle advantage of instruction queue is that, as next several instructions are usually in the queue, the BIU can access memory at a somewhat “leisurely” pace.

This means that slow-memory parts can be used without affecting overall system performance. Code segment CS is a bit register containing address of 64 KB segment with processor instructions. The processor uses CS segment for all accesses to instructions referenced by instruction pointer IP register.

CS register cannot be changed directly. The CS register is automatically updated during far jump, far call and far return instructions. Stack segment SS is a bit register containing address of 64KB segment with program stack. By default, the processor assumes that all data referenced by the stack pointer SP and bik pointer BP registers is located in the stack segment. SS register can be changed directly using POP instruction. Data segment DS is a bit register containing address of 64KB segment with program data.

Extra segment ES is a bit register containing address of 64KB segment, usually with program data.

What are the main blocks in BIU and EU of microprocessor? – Quora

By default, the processor assumes that the DI register references the ES segment in string manipulation instructions. To access instructions the uses the registers CS and IP. The CS register contains the segment number of the next instruction and the IP contains the offset. IP is updated each time an instruction is executed so that it will point to the next instruction. All general registers of the microprocessor can be used for arithmetic and logic operations.


The general registers are: This is accumulator register.

Architechture of

It gets used in arithmetic, logic and data transfer instructions. In manipulation and divisionone of the numbers involved must be in AX or AL.

This is micrpprocessor register. BX register is an address register. It usually contain a data pointer used for based, based indexed or register indirect addressing. This is Count register.

This serves as a loop counter. Program loop constructions are facilitated by it. This is data register.

It is also used in multiplication and division. This is stack pointer register pointing to program stack.

Microprocessor – 8086 Functional Units

It is used in conjunction with SS for accessing the stack segment. This is base pointer register pointing to data in stack segment. Unlike SP, we can use BP to access data in the other segments.

This is source index register which is used to point to memory locations in the data segment addressed by DS. By incrementing the contents of SI one can easily access consecutive memory locations. This is destination index register performs the same function as SI. There is a class of instructions called string operations, that use DI to access the memory locations addressed by ES.