Wilkes Design for Microprogrammed Control Unit: Basics and Working Explained | COA

Summary

In this video, the instructor explains the design and functioning of a Micro Programmed Control Unit. The video covers key aspects such as how programs are executed using control signals, instruction decoding, and micro-operations within the CPU. The instructor emphasizes the role of registers like the Instruction Register (IR) and Control Memory Address Register (CMAR) in controlling execution. Through detailed examples, the video clarifies how micro instructions are executed, addresses are generated, and conditional execution is handled. The video concludes by discussing the challenges and advantages of the proposed design, offering a comprehensive understanding of microprogramming in control units.

Takeaways

• 😀 The video explains the design of a micro-programmed control unit (MCU), which generates control signals for operations within a CPU.
• 😀 Before understanding the micro-programmed control unit, it is essential to know that programs are stored in external memory and are fetched by the CPU for execution.
• 😀 Programs consist of instructions stored in memory, which are fetched and decoded by the CPU for execution.
• 😀 Instructions in the CPU go through a process of identifying the operation to be performed, decoding, and executing through micro-operations.
• 😀 When a specific instruction is executed, the micro-operations are triggered by control signals generated from the instruction register (IR).
• 😀 The micro-programming design involves breaking down each instruction into smaller micro-operations that can be performed sequentially.
• 😀 Control signals are used to initiate the corresponding micro-operations and are generated based on the addresses provided by the control memory.
• 😀 Each micro-operation is executed step-by-step, and its address is provided by the instruction register (IR) along with other fields.
• 😀 The sequence of control signals ensures that the right micro-operations occur in the right sequence to execute the instruction properly.
• 😀 One challenge with this design is expanding control memory to handle larger instructions and store the necessary micro-programs, which may require a more extensive address field for larger systems.

Q & A

What is the primary function of a Micro Programmed Control Unit (MCU)?

The primary function of a Micro Programmed Control Unit (MCU) is to generate control signals that manage the execution of instructions in the CPU by performing micro-operations.

How does the CPU execute a program stored in memory?

The program is stored in memory, and the CPU fetches instructions from external memory. These instructions are then decoded and executed by the CPU, performing the necessary operations.

What are micro-operations, and why are they important in an MCU?

Micro-operations are small, low-level operations that are executed sequentially by the CPU for each instruction. They are essential because they break down complex instructions into simpler steps for execution.

What role does the Instruction Register (IR) play in instruction execution?

The Instruction Register (IR) stores the current instruction being executed. It provides the address for the first micro-instruction, which is then executed by the control unit.

How are control signals generated for micro-operations in the MCU?

The control unit generates control signals based on the decoded instruction. These control signals trigger the corresponding micro-operations to be executed by the CPU.

What is the significance of conditional execution in the context of MCU operation?

Conditional execution allows the control unit to decide the next micro-instruction address based on certain flags or conditions, like whether a result is zero or non-zero, allowing for dynamic control of the instruction flow.

How does the control unit decide the next micro-instruction's address?

The control unit decides the next micro-instruction's address based on the execution results of the previous instructions and any relevant conditional flags, like zero or non-zero outcomes.

What is the role of memory addressing in the execution of instructions?

Memory addressing allows the control unit to fetch instructions from memory by providing the correct addresses for each micro-instruction to be executed sequentially.

What are the advantages and disadvantages of the MCU's design?

The MCU's design is efficient in generating control signals for micro-operations, but it has a disadvantage of requiring multiple address fields for storing the next instruction's address, which increases memory usage.

How does control memory function in an MCU?

Control memory stores the addresses of the next micro-instructions. The control unit fetches these addresses to ensure the correct sequence of micro-operations is executed.