Memory Access/Write Back Cycle (if needed) - 5.1.4.1.5 | Module 5: Control Unit Design | Computer Architecture
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5.1.4.1.5 - Memory Access/Write Back Cycle (if needed)

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Introduction & Overview

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Quick Overview

The **Memory Access/Write Back Cycle** is the final phase for instructions that store results. The Control Unit places the target address in MAR, data in MDR, and initiates a memory write for STORE operations. For results destined for CPU registers, the CU enables the transfer of the ALU's output to the specified register. ### Medium Summary The **Memory Access/Write Back Cycle** is the concluding phase in an instruction's execution, occurring only when the computed result needs to be stored, either back into main memory (for `STORE` operations) or into a CPU general-purpose register. For memory writes, the Control Unit (CU) generates control signals to place the target memory address into the Memory Address Register (MAR) and the data to be written into the Memory Data Register (MDR), then initiates a `MEM_WRITE` command. If the result is meant for a general-purpose register, the CU orchestrates the transfer of the ALU's output (or an internal buffer's content) to the designated destination register, ensuring the CPU's state is updated correctly for the next instruction. ### Detailed Summary ### ● Memory Access/Write Back Cycle (if needed): If the instruction is a STORE operation or involves writing a result to memory, the CU generates signals to: * Place the target memory address into the MAR. * Place the data to be written into the MDR. * Initiate a memory write. If the instruction's result needs to be stored in a general-purpose register, the CU generates signals to enable the result's transfer from an internal buffer or ALU output to the specified destination register.

Standard

The Memory Access/Write Back Cycle is the concluding phase in an instruction's execution, occurring only when the computed result needs to be stored, either back into main memory (for STORE operations) or into a CPU general-purpose register. For memory writes, the Control Unit (CU) generates control signals to place the target memory address into the Memory Address Register (MAR) and the data to be written into the Memory Data Register (MDR), then initiates a MEM_WRITE command. If the result is meant for a general-purpose register, the CU orchestrates the transfer of the ALU's output (or an internal buffer's content) to the designated destination register, ensuring the CPU's state is updated correctly for the next instruction.

Detailed Summary

● Memory Access/Write Back Cycle (if needed):

If the instruction is a STORE operation or involves writing a result to memory, the CU generates signals to:
* Place the target memory address into the MAR.
* Place the data to be written into the MDR.
* Initiate a memory write.
If the instruction's result needs to be stored in a general-purpose register, the CU generates signals to enable the result's transfer from an internal buffer or ALU output to the specified destination register.

Detailed

● Memory Access/Write Back Cycle (if needed):

If the instruction is a STORE operation or involves writing a result to memory, the CU generates signals to:
* Place the target memory address into the MAR.
* Place the data to be written into the MDR.
* Initiate a memory write.
If the instruction's result needs to be stored in a general-purpose register, the CU generates signals to enable the result's transfer from an internal buffer or ALU output to the specified destination register.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • The Memory Access/Write Back Cycle is the final step for instructions that produce results requiring storage.

  • It handles two primary scenarios: writing data to main memory (STORE operations) or writing results to CPU general-purpose registers.

  • The Control Unit is responsible for generating all necessary control signals to manage address and data transfers to/from memory (via MAR and MDR) or directly to registers.