20.1. Computer Organization and Architecture: A Pedagogical Aspect

Welcome to the 7th unit of the module we are discussing, that is on the control circuitry of the computer. So, this is 7th unit in which we are going to study about micro instructions and micro-program.

This chunk introduces the unit's focus on micro instructions and micro-programming within computer control circuitry. It sets the stage for understanding how control signals can be generated in more flexible ways, shifting from traditional hardwired methods to programmable approaches.

Think of a remote control for a television. Traditional remotes have hardwired buttons for specific functions, just like hardwired control units. However, a smart remote can be programmed to perform various functions based on how you configure it, similar to micro-programmed control units.

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.

This chunk explains the difference between hardwired control units and microprogrammed control units. Hardwired control units use fixed logic circuits that generate control signals quickly but cannot be modified, whereas microprogrammed control units allow for flexibility by programming control signals into memory.

Imagine a light switch that’s hardwired to turn on a specific light. You cannot change its function easily without rewiring (like hardwired control). In contrast, a smart home system where you can program different lights to respond to commands is like a microprogrammed system, allowing for much more flexibility.

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...

Micro programs consist of sequences of micro instructions, which correspond to operations the CPU performs. Each micro instruction can control different aspects of the CPU, like setting specific bits to either 0 or 1 to execute a certain function.

Think of a recipe for a cake. Each step of the recipe represents a micro instruction. When you follow the recipe closely and in order, you create the cake (execute the program). Each instruction (step) contributes to the final outcome, just like each micro instruction contributes to achieving a specific operation in a computer.

...we allocate it separately for the micro programming based control. So, we call it as a micro-program memory...

Microprogram control memory is where the control signals corresponding to each micro instruction are stored. This allows for sequential fetching of control signals to direct the CPU operations. If the required signals are in memory, they can simply be retrieved when needed.

Imagine a library where each book contains instructions for various processes. When you need to know how to do something, you simply go to the correct book (memory location) and read the instructions. This approach mirrors how micro-program control units retrieve the necessary control signals.

...that is this control signals has to be generated in sequence...

Sequencing control signals involves navigating through the micro program memory to generate the right control signals in the correct order. While generating signals is straightforward because the required values are stored in memory, sequencing requires logic to handle jumps or loops within the program.

Consider following a map during a road trip. The regular route is straightforward (like sequential control), but if you encounter roadblocks and need to choose alternate paths (like jump instructions), you need to think carefully about your next move based on conditions, just like a microprogram counter that directs control flow.

Basically, we can also say that micro-program is very simple to a computer program. In case of a computer program the whole macro instructions are stored in a memory...

This chunk highlights the similarities between micro programs and traditional computer programs. Both use a form of memory to store instructions, but while macro instructions contain opcodes and operands for high-level operations, micro instructions directly translate into control signals for hardware control.

Think of a computer program as a construction blueprint. Each blueprint section has detailed instructions (macro instructions) for builders to follow. In contrast, micro programs can be seen as the individual steps taken by workers to assemble a structure, where each step directly translates to specific actions without needing interpretation.

--