20.3.3. Memory-based Logic

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.

A micro program is composed of a series of micro instructions. Each of these micro instructions corresponds to specific operations that the CPU needs to perform. Just like a recipe that lists steps one has to follow, a micro program lays out precise actions to manipulate data or control signals in the CPU. The purpose of these micro operations is to actually execute higher-level commands given by macro instructions, by breaking them down into smaller, manageable steps.

Think of a micro program as a detailed recipe for baking a cake. The macro instruction 'Bake a cake' is analogous to the macro instruction in the CPU. But, to execute this, you need to follow specific steps (like mixing, kneading, and icing), which represent the micro instructions in a micro program.

Micro-program control memory is very similar to a normal memory, but we allocate it separately for the micro programming based control.

Micro-program control memory stores the control signals necessary for executing micro instructions. This memory operates similarly to regular computer memory; however, it is specifically dedicated to microprogramming. Each location in this memory holds a set of control signals that will be activated when that specific part of the micro program is being executed, enabling the software to instruct the hardware directly.

Imagine the micro-program control memory as a tool kit where each tool (control signal) corresponds to a specific function (action) that you need for different tasks (instructions). Just like you wouldn’t keep all your tools mixed in with your regular items, this memory is organized separately to be accessed when executing micro instructions.

Generating the signals is very simple, that is just this values has to dumped from the memory and it has to go to the corresponding locations.

Control signal generation is a straightforward process in a micro-programmed control unit. When the control signals required to execute a micro instruction are stored in the micro-program control memory, these signals can be fetched directly when needed. This reduces complexity, as there is no need for extensive circuitry to generate these signals dynamically; they can simply be read from memory.

Think of generating control signals like looking up a phone number in your contact list. Instead of memorizing every number (which would take time and effort), you can simply pull it up from your phone. Similarly, the control signals can be fetched from memory, simplifying the operation.

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.

Sequencing refers to the order in which micro instructions are executed. While it is usually straightforward—moving sequentially from one micro instruction to the next—more complex operations like jump instructions require checking conditions before moving to a new instruction location. Thus, a micro-program counter helps to keep track of the current position in the micro program, enabling the control unit to branch to different parts of the program depending on previous operations or conditions.

Imagine following a video tutorial for a DIY project. Typically, you follow the steps one after the other. However, if the instructor mentions, 'If your results aren't as expected, skip to step 5,' you would need to jump around based on that condition. In micro programming, a similar decision-making process occurs that enables non-linear navigation through the instructions based on specific conditions.

Micro-programmed control is very flexible because, you can easily change the code if you like based on the requirements.

Micro-programmed control units are more adaptable than hardwired control units. While hardwired units use fixed circuits to generate control signals, making them faster but rigid, micro-programming allows for changes in control sequences by modifying the microprogram itself. This flexibility can be fundamental when adapting to various instructions or updates without altering the hardware.

Consider a factory assembly line. A hardwired setup is like machinery designed for one specific product—it works fast but can't be easily changed. In contrast, a micro-programmed setup is like a digital interface where you can change the production settings with the click of a button. This adaptability allows for efficiency and responsiveness to varying production needs.

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