REGISTERS

REGISTERS

Registers are group of flip-flops.

A single flip-flop can store one bit of information only.

* Registers are inside CPU.

 

TYPES OF REGISTERS

There are various types of registers -  


 

  

ACCUMULATOR  (Ac)

It is a 8 bit register.

It stores the Input or Output results.

 

         

PROGRAM COUNTER  (pc)

It is a 16 bit register.

It contains the address of the next instruction to be executed.

After an Instruction has been fetched, its contents are automatically incremented by 1 (pointing to the next instruction).

* Normally instructions are executed sequentially.

 

Increment of Program Counter by 1.

 

MEMORY ADDRESS REGISTER  (MAR)

It is a 16 bit register.

It holds the address of the next instruction to be fetched from the memory.

CPU (central processing unit) transfers the address of the next instruction from the program counter (pc) to the memory address register (MAR).

From MAR it is transmitted to the memory through the address bus. 

 

  

INSTRUCTION REGISTER  (IR)

Holds the current Instruction.

It holds instruction until it is decoded. 

 

MEMORY DATA REGISTER (MDR)

It holds data received from or sent to the memory.

It is connected to data bus.

* the flow of data from the CPU to the memory or from memory to the CPU is always through memory data register.