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19.3.2. Micro Program Based Control
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Welcome class! Today, we're diving into Micro Program Based Control. Can anyone tell me what roles micro instructions play in executing macro instructions?
Do micro instructions help divide complex tasks into simpler steps?
Exactly! They break down complex macro instructions into manageable micro steps using finite state machines. This ensures proper sequencing and timing of operations.
What are finite state machines?
Good question! Finite state machines are models that transition between a finite number of states based on inputs and conditions. They control how instructions are executed based on signals.
Can you give an example of a control signal?
Certainly! Control signals tell the system when to read from memory or when to update the program counter. For instance, when we execute ADD R1,M, specific signals activate to manage this operation.
I see! So it’s all about coordinating actions within the CPU, right?
Exactly! Each state represents a specific action in the instruction cycle, ensuring controlled execution.
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Let's discuss control signals in detail. Who can tell me some important control signals used in instruction execution?
There's the program counter output and memory address register?
That's right! The program counter (PC) sends the address of the current instruction to the memory address register (MAR). What happens next?
We then fetch the instruction from memory?
Exactly! And once we fetch, we need to properly load it into the instruction register using the appropriate signals. Can anyone name a signal that helps indicate that memory is ready?
Is it the Memory Function Complete (MFC)?
Correct! The MFC signal ensures that the data is ready before proceeding to the next instruction state.
So each signal corresponds to a specific action in the instruction life cycle?
Right again! Each control signal must be orchestrated perfectly to ensure smooth execution from one state to the next.
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Now, let's explore execution states further. How many states do you think an instruction like ADD R1,M goes through?
Could it be six or more?
Good estimate! Typically, such an instruction passes through several states, each governed by clock cycles. Each state completes a specific part of instruction execution.
What happens in state transitions?
Great question! Transitions depend on control signals indicating readiness from memory or the completion of a previous operation. For instance, if we’re waiting for MFC, we halt until it’s ready.
So the clock is a crucial part of timing decisions?
Yes, it orchestrates the flow of states and controls when to move to the next if the precedents are met.
Can a state be skipped then?
Usually no, unless there's an error condition or a specific branch instruction is invoked. Consistency is key in the FSM design.
"### Summary
Overview
Short Summary
Micro Program Based Control involves a series of control signals generated to execute macro instructions using finite state machines.
Medium Summary
This section discusses how micro instructions execute macro instructions through finite state machines, emphasizing the importance of control signals and their dependencies on clock cycles and external signals. It outlines various states in execution and the role of different registers.
Detailed Summary
Detailed Summary
In this section on Micro Program Based Control, we delve into the execution of instructions using micro-instructions generated through finite state machines (FSM). The primary focus is on the ADD instruction which demonstrates how data is transferred using control signals between registers and memory.
The section outlines a typical ADD instruction, represented as ADD R1, M, executed through a series of steps where the program counter (PC) and memory address register (MAR) are crucial. It starts with the program counter being incremented, with the initial signal being fed to the memory address register. The control signals generated during this process include outputs for operations such as reading and updating the program counter with the computed result from the arithmetic logic unit (ALU).
The execution is divided into distinct states, where each state corresponds to actions such as fetching instructions and waiting for external memory signals. The methodology employs a clock-driven FSM that requires precise timing and external signal readiness to transition from one state to another. Critical conditions, such as the readiness of memory flags, are described, and the interaction between internal control signals and external inputs is emphasized.
The importance of this control strategy lies in its efficiency in executing instructions quickly, albeit at a trade-off with complexity in design and flexibility, as each instruction has dedicated hardware in the control unit.
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Create a free accountSo, first let us take an example called ADD R1,M that is you are taking the memory location value R1 dumping it to R1 after adding it to whatever the content in R1.
Detailed Explanation
This chunk introduces the concept of micro program-based control by using an example of an instruction called ADD R1,M. In this instruction, the value from a specific memory location (denoted as M) is fetched and added to the value currently stored in the register R1. This sets the stage for understanding how micro instructions are executed at a lower level during the process of instruction execution in a CPU.
Examples & Analogies
Think of your favorite chef who prepares dishes by following a recipe. Instead of just knowing the final dish (the macro instruction), the chef understands the individual steps (micro instructions) like chopping, mixing, and cooking, which come together to create the final meal. Similarly, the ADD R1,M instruction can be broken down into smaller steps that the CPU follows to complete the task.
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Create a free accountIf you look forget about last class we have discussed that these are the series of control instructions, what are the signals involved? Program counter in, program counter out, Z, MFC all the signals whichever we are listed here are actually utilized for this micro-instruction.
Detailed Explanation
This section details the various signals involved in executing the ADD instruction. Key control signals like Program Counter (PC) in and out, the Z signal, and the Memory Function Complete (MFC) signal play critical roles in managing the flow of data and instructions in the CPU. The Program Counter holds the address of the next instruction to be executed, and these signals coordinate the steps of instruction execution and data handling.
Examples & Analogies
Imagine a traffic light system at a busy intersection. Just as traffic signals (like PC in and out) guide vehicles on when to stop or go, control signals in a CPU dictate when different components (like registers and memory) can send or receive data, maintaining a smooth flow of instruction execution.
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Create a free accountNow, first we will say if we remember that first was program counter out that is the PC value will be fed to the memory address register and then you will make it select zero, Add, Z.
Detailed Explanation
This paragraph breaks down how the CPU transitions between states during instruction execution. The PC value, which determines which instruction to fetch next, is passed to the Memory Address Register (MAR). The CPU must also configure the correct operations, represented by control signals such as 'select zero,' 'Add,' and 'Z.' These configurations inform the CPU about what operation to perform with the fetched data.
Examples & Analogies
Consider a librarian who needs to locate a book in a library. The librarian uses a catalog system (like the PC) to find the location of each book (passed to the MAR). The librarian then performs an action, such as 'place the book on the table,' which is akin to the CPU executing an operation based on the data retrieved.
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Create a free accountNow, we have to put it in PC that now PC is updated. Now, we have to it’s important we are waiting for an external signal this is an external signal.
Detailed Explanation
This part explains the necessity of waiting for external signals before proceeding with the instruction execution. After the PC value is updated, the CPU must often depend on external signals (like MFC) to proceed with the next steps. This waiting period is crucial, as it ensures that the data needed from memory is fully ready before the CPU continues its operations.
Examples & Analogies
Think about a waiter in a restaurant who cannot serve a dish until the chef says it’s ready. Even if the waiter has all the ingredients, they must wait for the chef's signal (external signal) before presenting the food. Similarly, the CPU must wait for external signals to ensure data integrity and readiness.
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Create a free accountAll these like PC, MAR, read, select 0, ADD, Z they are the control signals which you have to generate and then WFM, C is something on which you have to wait till you can go to the third stage.
Detailed Explanation
Control signals like PC, MAR, READ, SELECT 0, ADD, and Z, among others, are essential for guiding the execution of instructions. These signals effectively determine what actions are taken next in the instruction processing sequence. The WFM signal is particularly important, indicating that the CPU must wait for this signal before progressing to the next stage of operation.
Examples & Analogies
Imagine a construction team building a house. Each team member (control signals) has a specific task (like laying bricks, installing windows, etc.) and can only proceed when they receive the green light from the project manager (WFM signal). Without clear direction and timing, the workflow could become chaotic.
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Key concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
- Micro Instructions:
These are low-level instructions that detail specific operations for hardware execution.
- Finite State Machines:
Models that govern the sequential flow of executing instructions through states.
- Control Signals:
Commands that dictate the operations carried out in the CPU, such as reading and writing to memory.
- Program Counter:
A critical register that keeps track of the address of the next instruction to be executed.
- Memory Function Complete (MFC):
A signal indicating readiness of data from memory operations.
Examples
Step-by-step examples to apply the section's ideas and test your understanding.
An example of a micro instruction is the LOAD operation which specifies moving data from memory to a register.
During the execution of ADD R1, M, the instruction requires signaling the program counter to read the address of M, ensuring accurate execution.
Memory aids
Imagine a busy post office (the CPU) where the program counter is the postage label guiding each letter (instruction) to the next mailbox (execution state).
Flash Cards
Glossary
Micro Instruction
A low-level instruction that defines a single operation to be implemented in hardware.
Finite State Machine (FSM)
A computational model represented by states and transitions that define control flow in instruction execution.
Control Signal
Signals that manage the operations of the system, indicating actions like reading or writing from memory.
Program Counter (PC)
A register that maintains the address of the next instruction to be executed.
Memory Function Complete (MFC)
A control signal indicating that the memory operation has completed and data is ready.