20.3.2. Flexibility and Speed

Basically, in the last unit we have seen that basically how to generate the control signals, if the hardware for this is exactly fabricated as a hard-coded non-modifiable circuit. Which you actually call as the hardwired control unit, that that is the sequence of micro instructions and the control signals to be generated corresponding to that can be generated using a hard-coded circuit, which is synthesized from its finite state machine control.

A hardwired control unit is a type of control mechanism used in computers where the control signals are generated by a fixed, non-modifiable circuit. This setup is designed based on a finite state machine, which means the transitions and outputs are predetermined and cannot be altered during operation. It guarantees fast signal generation because the logic is implemented directly in hardware, thus removing any delays associated with fetching instructions from memory.

Think of a hardwired control unit as a traditional traffic light system. The sequence of lights (red, yellow, green) is fixed and cannot be changed on the fly. Just like the traffic light follows a preset order, a hardwired control unit follows a designated sequence of operations, making it very fast but inflexible.

In the next units basically, that is on micro-program control, that is these 2 units. So, basically, we are going to study how the same thing that is generation of the control signals can be done in a more flexible way and in terms of a program. So, it is not it’s very similar to what we understand by a normal computer program, which we have already looking throughout these lectures. But instead of the macro instructions we will be using micro instructions, and that control we will actually call micro-program based control.

Microprogrammed control units operate differently than hardwired ones. Instead of fixed signals, they generate control signals from stored programs (micro instructions). This allows for more flexibility, as the sequences can be changed simply by updating the program stored in memory. The concept is similar to how regular software (macro instructions) runs on a computer, with the micro instructions playing a similar role at a lower level of abstraction.

Imagine a chef following a recipe instead of a strict menu. The chef can alter the recipe (program) based on available ingredients (micro instructions), allowing for different dishes (control signals). This flexibility in cooking reflects how microprogrammed control units can adapt their operations based on changing program instructions, unlike hardwired systems that have a fixed approach.

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 few lectures back.

A micro program generates control signals that dictate the operations of a computer. Each micro program consists of a series of micro instructions, which correspond to smaller tasks that collectively accomplish a larger operation (macro instruction). When the macro instruction is processed, it triggers the sequence of micro instructions, allowing the control unit to execute complex operations in a manageable style.

Think of micro instructions like steps in a recipe. When you want to bake a cake (macro instruction), you need to follow multiple steps (micro instructions) — mixing batter, preheating the oven, pouring the mix, etc. Each step must be completed in sequence to achieve the final outcome, similar to how a micro program guides various small operations to execute a broader command.

So, sequencing actually slightly tricky, which is somewhat very easy in a finite state machine approach because there you have the flow of states which can take care very easily, but in this case, sequencing is slightly tricky, because unless until unless otherwise specified you will go from step 1 to step 2 to step 3 that is the sequential memory locations.

In a microprogrammed control unit, sequencing the execution of instructions can be more complicated than in a hardwired system. While a hardwired unit follows a clear, predetermined path through a finite state machine, a microprogrammed unit may need to 'jump' between non-sequential micro instruction locations based on conditions. This requires additional logic to evaluate when to branch in the program flow, complicating the control flow.

Imagine following a treasure map where sometimes you need to deviate from the indicated path based on clues (conditions). The hardwired approach is like a straight road where you keep driving forward, but the microprogrammed approach includes stops and detours to check for clues that might lead you off the main road towards the treasure.

--