Architecture of Microprocessor

Architecture of Generic Microprocessor:

  The microprocessor works as a heart of the system and performs primarily following functions:

• Fetch-decode-execute program instructions so as .
• Provides interrupt services to the external devices.
• Provides overall timing and control within the system.

 so as to execute a program, it must be loaded in memory. Microprocessor reads the primary instruction from memory and stores it into internal instruction register. it's referred to as fetching an instruction. After fetching an instruction, microprocessor interpretes it to find what instruction it is. This is known as decoding an instruction. Finally, microprocessor performs the work as indicated by an instruction, called executing an instruction, microprocessor repeats the same cycle for next instruction. It continues this until it is stopped when program ends. Thus, microprocessor repeatedly performs fetch-decode-execute cycle.

As program is stored in memory an instruction is fetched from memory by reading the memory. It is also possible that while executing a program microprocessor needs more data from memory or stores results into memory. Same way, it also can read data from any data input device like keyboard and send data to output device like printer. so as to satisfy all this microprocessor performs read and write operations with both memory also as I/O devices. we'll see these operations intimately afterward .

Architecture of Generic Microprocessor

The microprocessor also provides services to external hardware devices or request by executing special programs called Interrupt Service Routines (ISRs). For example, keyboard service is executed to read a key code from keyboard when a key's pressed. It plays supervisory role and control all the devices.

The three hardware sections registers, ALU and control and timing are responsible for above functions. Let us study the architecture of generic microprocessor which explores three sections further. It is given in figure.

The functions of each block are discussed as follows:

Arithmetic and Logical Unit: it performs all the arithmetic and logical operations. It consists of logic circuits like adder, shifter etc.

Accumulator: it's a special register utilized in all the arithmetic and logic operations. The results of arithmetic and logical operation is stored in accumulator. Accumulator also acts as a source for one among the operands when arithmetic or logic operations is performed.

Temporary register: it provides another operand to ALU for arithmetic and logic operations.

Status register: it stores the status of execution of last arithmetic or logic instruction. It includes normally overflow during addition, parity of result, sign of the number, whether result was zero etc. the status register consists of individual flip-flops for each flag like overflow, parity, sign, zero etc. The contents of these flags are used to decide flow of execution of the program.

Stack pointer: the stack is LIFO memory employed by program to store values temporarily, during the execution. The stack pointer register stores the address of last location in stack where the last value is stored. so it are often read first. it's also referred to as top of the stack, because it points to top of stack.

Instruction register and Instruction decoder: the microprocessor repeatedly performs fetch-decode-execute cycle. The microprocessor while fetching the instruction from memory, brings it into instruction register. The instruction decoder decodes the instruction stored in the instruction register and sends necessary signals to timing and control section to execute the instruction.

Program counter: it stores the address of next instruction to be executed. The program counter sequences the execution of program. Once the previous instruction is completed, the microprocessor fetches the next instruction from the address stored in program counter.

General purpose registers: Microprocessor contains no. of general purpose registers which are used to store data or address.

Timing and control: This section controls all the operations performed by the microprocessor as well as provides the necessary synchronization for performing operations. It is also liable for generating/reading various control signals necessary to perform operations with external devices like memory or I/O devices.

Internal bus and buffers: Internal bus provides necessary paths to allows the transfer of knowledge from one component to a different . Buffers provide necessary buffering.