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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.
"### Summary
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.
"### Summary
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
These are low-level instructions that detail specific operations for hardware execution.
Models that govern the sequential flow of executing instructions through states.
Commands that dictate the operations carried out in the CPU, such as reading and writing to memory.
A critical register that keeps track of the address of the next instruction to be executed.
A signal indicating readiness of data from memory operations.
To remember PC, just see, it tracks where to be, next instruction's key!
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).
C-S-P-M for 'Control Signals', 'States', 'Program Counter', and 'Memory Completion'.
M-F-C for 'Memory Function Complete', the signal that tells us when memory operations are done.
Term
What is a micro instruction?
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Term
What does the program counter (PC) keep track of?
Click to flip
A low-level instruction that defines a single operation to be implemented in hardware.
A computational model represented by states and transitions that define control flow in instruction execution.
Signals that manage the operations of the system, indicating actions like reading or writing from memory.
A register that maintains the address of the next instruction to be executed.
A control signal indicating that the memory operation has completed and data is ready.
Micro Program Based Control involves a series of control signals generated to execute macro instructions using finite state machines.
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.
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.