INTRODUCTION TO MICROPROCESSORS

What is microprocessor? Draw an internal block diagram of a register based microprocessor

and explain its operations.      .

Microprocessor : With the advent of semiconductor technology, it is possible to integrate the CPU in a single^. chip. The result is the microprocessor. Metal oxide semiconductor (MOS) technology is typically used to fabricate the standard off-the-shelf microprocessors. The microprocessor is comprised of a register section, one or more ALUs and a control unit.

Execution Unit ( EU )      BUS INTERFACE UNIT ( BIU )

Figure-1 : Internal block diagram of register based microprocessor 8086.

Figure-1 shows a block diagram of a register based microprocessor '8086. The 8086 is internally divided into two separate functional units :

i)                    Bus Interface Unit (BIU)

ii)                  Execution Unit (EU)

These two units function .independently. They are described below :

i)       Bus Interface Unit BIU : this unit fetches instructions, reads data from memory and ports,
and writes data to memory and I/O ports. The BIU interfaces the 8086 to the outside world. It contains

·     Instruction pointer

·     Instruction queue : The BIU's instruction queue is a First-In-First-Out (FIFO) group of registers in

Which up  to six bytes of instruction code are prefetched from memory ahead of time.

®      Address generation bus control circuitry : It provides functions such as fetching and queuing of instructions, and bus control. It generates all the bus control signals such as read and write signals for memory and I/0.

4, Segment registers The BIU has four (CS, DS, SS, ES)16-bit segment registers. The segments can be contiguous, partially overlapped, fully overlapped. or disjoint.

Execution unit : The EU decodes and executes instructions. It consists of the following

·        A decoder in the EU control system translates instructions the .

·        The EU has a 16-bit ALU for performing arithmetic and logic operations.