The Heart of Computer Organization & Architecture
Think of Computer Organization & Architecture like building a city:
The city's blueprint—the grand design of CPU, memory, buses.
How all those streets, power lines, and traffic lights are actually built and connected.
The neighborhood where the CPU's actual work happens, teaching you how to speak directly to the hardware using assembly language.
Long ago, programmers only had machine language—strings of 0s and 1s. That's like giving directions in pure GPS coordinates—accurate but painful.
Assembly language came as a blessing: short English-like words (mnemonics) such as ADD or MOV that the computer can convert into those 0s and 1s.
An Assembler acts like a translator:
Code in mnemonics (ADD, MOV, etc.)
Translates to machine code (0s and 1s)
Executes the machine code instructions
The 8085 microprocessor is like a small but smart clerk with specific "drawers" to store things:
| Part | Role (Story Version) |
|---|---|
| Accumulator (A) | The main calculator's tray—every add, subtract, AND, OR result lands here. |
| Registers B,C,D,E,H,L | Six little notepads to keep temporary numbers; some can pair up for 16-bit tasks. |
| Flag Register | Mood indicators: Zero, Carry, Sign—telling if the last math was zero, overflowed, etc. |
| Program Counter (PC) | A bookmark pointing to the next instruction to read. |
| Stack Pointer (SP) | Manages a vertical pile (stack) for saving return addresses when we jump to subroutines. |
Think of the 8085 as a small office with a main desk (Accumulator), several notepads (registers), a flag system to track status (Flag Register), a bookmark for where you left off (Program Counter), and a stack of papers to save your place when working on different tasks (Stack Pointer).
The 8085 understands instructions grouped like this:
Move or copy data (MOV, MVI, LDA, STA)
Add, subtract, increment, decrement (ADD, SUB, INR, DCR)
AND, OR, XOR, compare (ANA, ORA, CMP)
Change the story's flow—jumps, calls, returns (JMP, CALL, RET)
Halt, enable interrupts, push/pop data
Instructions can be 1, 2, or 3 bytes long depending on how much extra info (like addresses) they carry:
Operations that don't need extra data, like MOV A,B or RLC
Operations that need an 8-bit data value, like MVI A,05H
Operations that need a 16-bit address, like LDA 2050H
Imagine you need the 8085 to add two numbers from memory:
Program Counter tells CPU where to look for the next instruction
Instruction is read, e.g., ADD M, and the CPU understands what to do
ALU adds the number from memory to the Accumulator
Zero or Carry flags flip if needed based on the result
PC moves to the next instruction—unless a jump changes the path
Here's a simple program that adds two numbers stored at memory locations 2050H and 2051H:
Understand the problem requirements
Develop a step-by-step solution
Create a visual representation of the algorithm
Write the program using 8085 mnemonics
Convert to machine code and run on the processor
For the CPU to talk to memory smoothly, memory interfacing is the roadway design:
Tells where in memory to read from or write to
Carries the actual what—the data being transferred
Read/Write, Chip Select signals act like traffic lights
Think of memory interfacing like a city's transportation system. The address bus is like street signs telling you where to go, the data bus is the vehicles carrying people or goods, and the control signals are traffic lights and road signs that direct the flow. Efficient interfacing means fast, reliable data flow—critical for program speed and overall system performance.
Ensuring the correct memory chip is selected for each address range
Coordinating the timing of signals to ensure reliable data transfer
Ensuring proper power supply to memory chips for stable operation
8085 registers, buses, and memory connections show you CPU internals. When you program the 8085, you're directly manipulating these hardware components, giving you a ground-level view of how computers work at the most fundamental level.
The fetch-decode-execute cycle reveals how any processor, not just 8085, runs software. Understanding this cycle is essential to grasping how computers perform tasks at the most basic level. Every modern CPU, no matter how complex, still follows this same fundamental process.
Writing assembly teaches how high-level languages eventually translate to efficient hardware operations. When you write in C++ or Python, the code is compiled down to machine instructions similar to what you write in 8085 assembly. Understanding this connection helps you write more efficient high-level code.
8085 programming demonstrates the critical interface between software and hardware. It shows how abstract software concepts are implemented in physical hardware, a fundamental concept in computer architecture that remains relevant regardless of how technology advances.
In short, this unit is like a guided adventure into the heart of a microprocessor. By writing assembly for the Intel 8085, you learn to think like the CPU itself—seeing how every high-level program eventually becomes a precise dance of instructions, buses, and memory.
| Aspect | Key Points |
|---|---|
| Purpose | Control hardware directly, write optimized code. |
| 8085 Core | Accumulator, six registers, PC, SP, Flag register. |
| Instruction Types | Data transfer, arithmetic, logical, branching, control. |
| Memory Interfacing | CPU ↔ Memory communication using buses & control lines. |
| Program Steps | Analyze → Algorithm → Flowchart → Assembly code → Assemble → Execute. |
| COA Link | Demonstrates CPU organization, instruction cycle, hardware–software bridge. |
Learning 8085 assembly programming is like learning the native language of computers. It gives you a fundamental understanding of how software interacts with hardware at the most basic level. This knowledge forms the foundation for understanding more complex computer architectures and for writing efficient, optimized code in any programming language.
While modern processors are vastly more complex, the principles you learn with the 8085 remain relevant. Understanding assembly language helps in fields like embedded systems programming, operating system development, compiler design, and performance-critical applications where direct hardware control is essential.