Date: 9 Apr 2013

Some registers in microprocessor are utilized by ALU and the control section for temporary storage of instruction, operands or address at various stages of instruction execution

Memory Address Register

Memory Address Register (MAR) stores the address information to be communicated to the outside world. The information is stored temporarily.

Instruction Register

An instruction fetched from the memory is temporarily stored in instruction register (IR) prior to its decoding.

Memory Buffer Register

The information to be stored into the memory is temporarily stored in memory buffer register (MBR). The item to be received from the memory is also temporarily stored in the MBR by the memory controller.

Temporary Registers

The ALU section is provided with one or more temporary register. These registers are used to store temporary results when ALU performs the arithmetic and logic operations. They hold operands or addresses that are part of an instruction.

For example, the registers W and Z are of 8 bit registers. When a 3 byte instruction containing a 2 byte address is to be fetched from memory into the microprocessor, the first byte, i.e., opcode is placed in the IR by the first memory reference. Two additional memory references obtained the two address bytes, which are placed in the temporary registers, W and Z. During instruction execution, the address in W and Z is transferred to MAR.