Which register in 8086 contains the address of the next instruction to be fetched?

What register points to the next instruction?

actually register holds the data..there are 6 register which are temporary registers..program counter holds the address of next instruction to be fetched..instruction register holds the currently executed data...

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

What registers is used to keep track of address of the memory location where the next instruction is located?

Instruction pointer (IP) is used to hold the offset of the next instruction to be fetched for BIU available from Code Segment whose base address is held in CS segment base register..

How you calculate the physical address in 8086 microprocessor with example?

The physical address in the 8086/8088 is calculated by adding the effective address with the contents of one of the segment registers left shifted by 4 bit positions. This results in a 20 bit address bus. As an example, if the CS register contains 1234H, and the IP register contains 5678H, then the next instruction is fetched from physical address 179B8H, which is 1234H times 16 (12340H) plus 5678H. The segment register used is selected by context, or by using a segment override prefix, however, the code segment register (CS) can not be overidden during instruction fetch, nor can the stack segment register (SS) be overidden during stack pushes and pops.

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 is the definition of fetch cycle?

Fetch cycle is defined as a part of instruction cycle in which data is fetched from the memory pointed by Holds the address of a memory block to be read from or written to) and stores the data in MDR( a two-way register that holds data fetched from memory (and ready for the CPU to process) or data waiting to be stored in memory) for further processing. Instruction cycle= Fetch cycle+ Execute cycle

What is defference between direct and indirect address?

Direct addressing involves specifying the exact memory address where data is stored or fetched. Indirect addressing involves using a memory address that points to where the data is stored or fetched. In direct addressing, the actual data is accessed, while in indirect addressing, a reference to the data's location is accessed.

What is a fetch as a cycles in a CPU?

The first part of the instruction execution cycle is the fetch cycle. Tnstruction cycle Each computer's CPU can have different cycles based on different instruction sets, but will be similar to the following cycle: 1. Fetch the instruction The next instruction is fetched from the memory address that is currently stored in the Program Counter (PC), and stored in the Instruction register (IR). At the end of the fetch operation, the PC points to the next instruction that will be read at the next cycle. 2. Decode the instruction The decoder interprets the instruction. During this cycle the instruction inside the IR (instruction register) gets decoded. 3.In case of a memory instruction (direct or indirect) the execution phase will be in the next clock pulse. If the instruction has an indirect address, the effective address is read from main memory, and any required data is fetched from main memory to be processed and then placed into data registers(Clock Pulse: T3). If the instruction is direct, nothing is done at this clock pulse. If this is an I/O instruction or a Register instruction, the operation is performed (executed) at clock Pulse. 4. Execute the instruction The Control Unit of CPU passes the decoded information as a sequence of control signals to the relevant function units of the CPU to perform the actions required by the instruction such as reading values from registers, passing them to the ALU to perform mathematical or logic functions on them, and writing the result back to a register. If the ALU is involved, it sends a condition signal back to the CU.

What is address sequencing in computer organization?

Microinstructions are stored in control memory in groups, with each group specifying routine. Each computer instruction has its own microprogram routine in control memory to generate the microoperations that execute the instruction. The hardware that controls the address sequencing of the control memory must be capable of sequencing the microinstructions within a routine and be able to branch from one routine to another. To appreciate the address sequencing in a microprogram control unit, let us enumerate the steps that the control must undergo during the execution of a single computer instruction. An initial address is loaded into the control address register when power is turned on in the computer. This address is usually the address of the first microinstruction that activates the instruction fetch routine. The fetch routine may be sequenced by incrementing the control address register through the rest of its microinstructions. At the end of the fetch routine, the instruction is in the instruction register of the computer. The control memory next must go through the routine that determines the effective address of the operand. A machine instruction may have bits that specify various addressing modes, such as indirect address and index registers. The effective address computation routine in control memory can be reached through a branch microinstruction, which is conditioned on the status of the mode bits of the instruction. When the effective address computation routine is completed, the address of the operand is available in the memory address register. The next step is to generate the microoperations that execute the instruction fetched from memory. The microoperation steps to be generated in processor register depend on the operation code part of the instruction. Each instruction has its own microprogram routine stored in a given location of control memory. The transformation from the instruction code bits to an address in control memory where the routine is located is referred to as a mapping process. A mapping procedure is a rule that transforms the instruction code into a control memory address. Once the required routine is reached, the microinstructions that execute the instruction may be sequenced by incrementing the control address register, but sometimes the sequence of microoperations will depend on values of certain status bits in processor registers. Micro programs that employ subroutines will require an external register for storing the return address. Return addresses cannot be stored in ROM because the unit has no writing capability. When the execution of the instruction is completed, control must return to the fetch routine. This is accomplished by executing an unconditional branch microinstruction to the first address of the fetch routine. In summary, the address sequencing capabilities required in control memory are: 1. Incrementing of the control address register. 2. Unconditional branch or conditional branch, depending on statues bit conditions. 3. A mapping process from the bits of the instruction to an address for control memory. 4. A facility for subroutine call and return.

What is 6 stage instruction pipelining?

1. FI (fetch instruction) - get the next instruction 2. DI (decode instruction) - decode the opcode and operands 3. CO (calculate operands) - calculate EA of the operands 4. FO (fetch operands) - fetch operands from memory (not necessary for register data) 5. EI (execute instruction) - execute instruction storing result if necessary 6. WO (write operand) - write the result in MEM

What is the function of Data Register?

holds 16 bit data just fetched from the memory

Which register in 8086 contains the address of the next instruction to be fetched?

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What is the consists in the Instruction register?