20.2. Unit Summary

Basically, if the control signals are generated from a dedicated circuit we call it as a hardwired control. And alternative approach is basically which we can generate such signals which are basically programmed into some kind of a memory. So, it is if it is a memory-based logic in which each of the memory cells or each of the memory word has the corresponding control signals to be generated, then that approach is actually called the micro-programmed control unit.

In this chunk, we are talking about two methods of generating control signals in a computer system. The first method is called hardwired control, which relies on a fixed circuit to generate control signals. This means that once the circuit is made, it cannot be changed. The second method is micro-programmed control, where the control signals are stored in memory. This allows for flexibility because we can change the commands in memory without physically altering the circuit. Essentially, hardwired control is fast but inflexible, while micro-programmed control is slower but offers greater adaptability.

Think of hardwired control as a traditional light switch system in a home that's designed specifically for each light in the room. If you want to add more lights or change their positions, you need to rewire the entire system. On the other hand, micro-programmed control is like a smart home system where you can change how the lights behave through an app or software, without needing to change the physical wiring.

So, basically a micro program consists of a sequence of instructions, and basically these instructions are nothing but which are the basically a micro-program corresponding to a basically a sequence of micro operations that is very well known, that a macro instruction has some micro instructions which we have already discussed a few lectures back.

Here, we learn about micro-programs and how they relate to micro operations. A micro program is a set of instructions that the computer follows, similar to steps in a recipe. Each macro instruction, which we refer to as a larger command, can break down into smaller commands called micro instructions. These micro instructions are then executed in sequence, allowing for complex operations to be performed in a detailed manner. The flexibility of micro-programs comes from the fact that the instructions are stored in a memory designed specifically for this purpose, known as micro-program memory.

Imagine a cooking recipe (the macro instruction) that lists out several steps for preparing dinner. Each step (micro instruction) must be followed in order, like washing vegetables, chopping them, and sautéing them. If you forget a step, you can easily go back and check the recipe. This flexibility is similar to how micro-programs allow for adjustments in computer instructions stored in their respective memory.

So, basically a micro-program control unit is a simple logical circuit. In fact, it’s a memory with some peripheral circuits, which actually will go through sequence of micro instructions.

The micro-program control unit functions by using a basic logical structure combined with memory capabilities. This allows the system to execute a series of micro instructions sequentially. When a micro instruction is fetched from memory, it directly influences the control signals generated for that operation. The sequencing refers to the order in which these micro instructions are executed. If executed in sequence, the system follows a linear path through memory. However, if the instruction requires a jump or a branch (like skipping a few steps in a recipe), the system must have additional logic in place to handle that. This adds a layer of complexity to maintaining an orderly flow of operations.

Think of the micro-program control unit like an assembly line in a factory where each worker has specific tasks. Each worker (micro instruction) must complete their task in the correct order to keep the production flowing smoothly. If a worker needs to skip ahead to address a problem (a jump in sequencing), a supervisor must coordinate this, which adds complexity but ensures that production can adapt to changes.

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