Hardwired vs microprogrammed control

Summary

This video script discusses two strategies for implementing control units in a microprocessor: hardwired control and microprogrammed control. Hardwired control uses a finite state machine to generate control signals for instruction execution, while microprogrammed control encodes control signals into compact micro instructions, forming a micro program stored in memory. Both approaches aim to manage the data path's operations effectively.

Takeaways

• 💡 Hardwired Control Unit and Micro Program Control Unit are two strategies for implementing control in a processor.
• 🔍 The control unit is responsible for generating control signals necessary for the data path to perform operations.
• 📡 The data path includes components like the bus and registers, which are controlled by the control signals.
• 🛤️ Instructions are translated into a sequence of control signals, which are like an array of multiple signals.
• 🔄 A control unit generates a predefined sequence of control signals for each instruction execution.
• 🏗️ Hardwired control uses a finite state machine with combinational logic to produce control signals based on the instruction register and calculation status.
• 🔑 The finite state machine in hardwired control contains the logic to generate the sequence of signals.
• 📝 Micro Program Control Unit uses micro instructions, which are compact codes representing sets of control signals.
• 🔀 A micro program is a sequence of micro instructions that execute to perform an instruction.
• 💾 The micro program is stored in memory and is interpreted by the microprocessor to generate the appropriate control signals.
• 🔄 Both approaches result in the generation of control signals, but microprogramming encodes them into a program stored in memory.

Q & A

What are the two strategies for implementing control in a processor as mentioned in the script?

The two strategies for implementing control in a processor are hardwired control unit and micro program control unit.

What is a hardwired control unit?

A hardwired control unit is a finite state machine that uses a block of combinational logic to generate control signals needed for executing instructions. It directly translates instructions into a sequence of control signals.

How does the hardwired control unit generate control signals?

The hardwired control unit generates control signals by traversing a predefined sequence of states, changing zeros and ones to produce different arrays of control signals at each point in time.

What is a micro program control unit?

A micro program control unit uses a sequence of micro instructions, each corresponding to a set of control signals, to generate the necessary control signals for executing instructions.

How does a micro instruction differ from a regular instruction?

A micro instruction is a compact code that encodes a set of control signals required to control the data path, whereas a regular instruction is a higher-level command that the processor needs to execute.

What is the role of the micro program in a micro program control unit?

The micro program is a sequence of micro instructions that, when executed, generates the control signals needed for the data path to perform the operations required by a given instruction.

How does the control unit decide which sequence of control signals to generate?

In a hardwired control unit, the decision is made by the finite state machine logic based on the instruction register and calculation status. In a micro program control unit, the instruction register determines which micro program to execute.

What is the advantage of using a micro program control unit over a hardwired control unit?

A micro program control unit offers flexibility and ease of modification since the control sequences are stored in memory and can be changed by updating the micro program, whereas hardwired control units require changes to the hardware logic.

How does the control unit ensure that the data path performs the required operations?

The control unit ensures that the data path performs the required operations by generating a sequence of control signals that activate the necessary components of the data path at the correct times.

What is the significance of the instruction register in the context of control units?

The instruction register holds the current instruction that the processor is executing, and its value determines the sequence of control signals generated by the control unit, either through the finite state machine in a hardwired control unit or the micro program in a micro program control unit.

Can you provide an example of how a control signal array might look like in a hardwired control unit?

A control signal array might look like an array with multiple signals, where some signals need to be active at certain times, such as [1, 0, 0, 1] at one step and [0, 1, 1, 0] at the next step, representing the activation of different components of the data path.