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In the 8086 microprocessor, the Instruction Pointer (IP) register contains the address of the next instruction to be fetched and executed. It works in conjunction with the Segment Registers (such as CS - Code Segment) to form the complete address of the instruction in memory. The IP is automatically updated as instructions are executed, ensuring that the CPU always knows where to fetch the next instruction from.
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What is Function of IP register in 8086?
The IP register contains the address of the next instruction to fetch and execute. Normally, IP is incremented by the number of bytes in the instruction after execution of that instruction, unless a transfer of control occurs, in which case IP is loaded with a new value.
What is the name of the cycle in which an instruction is taken from memory and loaded into the instruction register?
Fetch
What is opcode fetch?
The process of transferring instruction codes from memory location to instruction queue register is called opcode fetch.
How would you describe the fetch execute cycle?
Fetch Execute Cycle A more complete form of the Instruction Fetch Execute Cycle can be broken down into the following steps: 1. Fetch Cycle 2. Decode Cycle 3. Execute Cycle 4. Interrupt Cycle 1. Fetch Cycle The fetch cycle begins with retrieving the address stored in the Program Counter (PC). The address stored in the PC is some valid address in the memory holding the instruction to be executed. (In case this address does not exist we would end up causing an interrupt or exception).The Central Processing Unit completes this step by fetching the instruction stored at this address from the memory and transferring this instruction to a special register - Instruction Register (IR) to hold the instruction to be executed. The program counter is incremented to point to the next address from which the new instruction is to be fetched. 2. Decode Cycle The decode cycle is used for interpreting the instruction that was fetched in the Fetch Cycle. The operands are retrieved from the addresses if the need be. 3. Execute Cycle This cycle as the name suggests, simply executes the instruction that was fetched and decoded
What are the four distinct actions that a machine instruction can specify?
• The processor fetches the instruction from memory • Program counter (PC) holds address of the instruction to be fetched next • PC is incremented after each fetch • Fetched instruction loaded into instruction register
How does fetch decode cycle work?
The program counter in the processor holds the address of the next instruction needed from main memory. The program counter copies its contents into the memory address register. The memory address register then sends the address along the address bus to main memory and the contents of the memory location specified by the address are sent along the data bus to the memory buffer register. The contents of the memory buffer register are then copied to the current instruction register where they are decoded and executed.
How does the Fetch Decode Execute work?
The program counter in the processor holds the address of the next instruction needed from main memory. The program counter copies its contents into the memory address register. The memory address register then sends the address along the address bus to main memory and the contents of the memory location specified by the address are sent along the data bus to the memory buffer register. The contents of the memory buffer register are then copied to the current instruction register where they are decoded and executed.
What is the Process (Fetch Decode Execute Store)?
The program counter in the processor holds the address of the next instruction needed from main memory. The program counter copies its contents into the memory address register. The memory address register then sends the address along the address bus to main memory and the contents of the memory location specified by the address are sent along the data bus to the memory buffer register. The contents of the memory buffer register are then copied to the current instruction register where they are decoded and executed.
How does fetch decode execute cycle work?
The program counter in the processor holds the address of the next instruction needed from main memory. The program counter copies its contents into the memory address register. The memory address register then sends the address along the address bus to main memory and the contents of the memory location specified by the address are sent along the data bus to the memory buffer register. The contents of the memory buffer register are then copied to the current instruction register where they are decoded and executed.
Where does the address operand of the instruction copied?
The address operand of an instruction is typically copied into the instruction register (IR) during the instruction fetch phase of the instruction cycle. From the IR, the operand can be accessed by the control unit or the arithmetic logic unit (ALU) for execution. In some architectures, the address operand may also be stored in specific registers, depending on the instruction type and the addressing mode used.
What is the difference between a direct and indirect address instruction how many references to memory are needed for each type of instruction to bring an operand into a processor register?
Direct address instructions specify the memory location of the operand directly within the instruction itself, requiring only one memory reference to fetch the operand. In contrast, indirect address instructions specify a memory location that contains the address of the operand, necessitating two memory references: one to retrieve the address and another to fetch the operand itself. Therefore, direct addressing is more efficient in terms of memory access.
How do the contents of the MAR and MDR registers changes during the fetch decode execute cycle?
During the fetch-decode-execute cycle, the Memory Address Register (MAR) holds the address of the memory location from which data is to be fetched or to which data is to be written. In the fetch phase, the MAR is loaded with the address of the next instruction to be executed. The Memory Data Register (MDR) then temporarily holds the data fetched from memory or the data to be written to memory. As the cycle progresses, the contents of the MAR and MDR are updated based on the memory operations required for executing the instruction.
