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In assembly language, a backward reference is when a program refers to a label or memory location that appears earlier in the code. This is commonly used for implementing loops or conditional jumps where the target instruction is located before the jump instruction in memory. Backward references are resolved during the assembly process to calculate relative offsets.
The possible states that define an instruction execution are as follows: Instruction address calculation - Determine the address of the next instruction to be executed. Instruction fetch - Read instruction from its memory location into the processor. Instruction operation decoding - Analyze instruction to determine type of operation to be performed and operand to be used. Operand address calculation - If the operation involves reference to an operand in memory or available via I/O, then determine the address of the operand. Operand fetch - Fetch the operand from memory or read it in from I/O. Data operation - Perform the operation indicated in the instruction. Operand store - Write the result into memory or out to I/O.
Load instruction means to load the instruction from the memory to the processor (accumulator).. But store instruction is opposite of it,it stores information from accumulator to the memory.
The instructions have to remain in memory at all times while the program is running. They get there by loading the entire program into memory. The CPU's instruction registers keep track of the current instruction and the next instruction.
When an instruction is read from memory, it is called "fetching." This process is part of the instruction cycle, where the Central Processing Unit (CPU) retrieves an instruction from memory to execute. Fetching is the initial step, followed by decoding and executing the instruction. This sequence is essential for the proper functioning of a computer's processing capabilities.
Memory address FFFF0h is the memory address always assigned to the first instruction in the ROM BIOS
The instruction opcode is a type of data contained in memory, pointed to by the PC (Program Counter) register.
Fetch
Indirect addressing needs 2 reference to memory
twice
1.Fetch the most instructions from memory. 2.Read an apparend if required by the instruction.(Apparend is a quantity to be operated as directed by its associated instruction.) 3.Execute the instruction.(Do what the instruction says.) 4.Write the result backe into memory.(If required by instruction.)
In an instruction cycle with indirect addressing, the CPU fetches the instruction, decodes it to determine the memory address of the operand stored in a register, fetches the operand from the memory location pointed to by the register, and executes the instruction using the operand. Finally, the CPU stores the result back in memory if needed. This extra step of fetching the operand based on the indirect memory address adds complexity to the instruction cycle.