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An Introduction to the Advanced Microprocessors
Introduction
Microprocessor Specifications
Microcontroller
Introduction to Microcomputer
Block Diagram of Microcomputer
Arithmetic Logic Unit (ALU)
Registers
Program Counter
Instruction Decoder
Timing and Control Section
Bus Buffers and Latches
Internal Buses and Control Lines
Control Inputs/Outputs
Interrupt Control
Functional Pin Diagram of 8085
Address Bus
Multiplexed Address/Data Bus
Control & Status Signals
Power Supply and Frequency Signals
Externally Initiated Signals
Serial I/O Ports
Addressing I/O Devices
Functional Block Diagram of 8085
Types of Buses (three types)
ALU
Flags
Registers
Interrupts
Serial I/O
Program Counter & Stack Pointer
Incrementer-Decrementer
Instruction Decoder
Implied Addressing
Register Addressing
Immediate Addressing
Direct Addressing
Register-Indirect Addressing
A microprocessor is the CPU (Central Processing Unit) of a computer, fabricated on a single integrated circuit (IC) chip.
It performs arithmetic, logical, control, and input/output (I/O) operations.
Example: Intel 8085, Intel 8086, Pentium, AMD Ryzen etc.
Microprocessors are classified into generations:
1st Generation (1971-1973):
Example: Intel 4004, 8008
4-bit, small instruction sets, very limited speed and memory.
2nd Generation (1974-1978):
Example: Intel 8080, 8085
8-bit, better instruction sets, support for small computers.
3rd Generation (1979-mid 80s):
Example: Intel 8086, 80186, Motorola 68000
16-bit, improved performance, introduction of memory segmentation.
4th Generation (mid 80s-1990s):
Example: Intel 80286, 80386, 80486
32-bit processors, virtual memory, multitasking.
5th Generation & Later (1990s-present):
Example: Pentium series, Core series, AMD Athlon, Ryzen, Apple M-series
64-bit, multicore processors, high clock speeds, advanced instruction sets, AI/ML support.
When comparing advanced microprocessors, we look at:
Word Length (8-bit, 16-bit, 32-bit, 64-bit)
Clock Speed (measured in MHz or GHz)
Instruction Set (CISC, RISC, ARM etc.)
Data Bus & Address Bus Width (decides memory addressing capability)
Cache Memory (L1, L2, L3 for speed)
Power Consumption & Heat Management
Microprocessor → CPU on a chip (needs external memory & I/O devices). Used in PCs, laptops, servers.
Microcontroller → CPU + memory + I/O ports on a single chip. Used in embedded systems like washing machines, cars, medical devices.
Enable high-speed computing (billions of instructions per second).
Support multimedia, networking, AI, gaming, simulations.
Used in desktops, laptops, mobile phones, IoT devices, robotics, space research.
✅ In your HSC exams, usually 3-4 mark questions are asked like:
Define microprocessor.
List generations of microprocessors with examples.
Difference between microprocessor and microcontroller.
State any two specifications of advanced microprocessors.
A microcomputer is a computer built around a microprocessor (CPU on a single chip).
It is smaller, cheaper, and less powerful than minicomputers or mainframes.
First appeared in the 1970s with Intel 8080/8085 processors.
Examples: Personal computers (PCs), laptops, embedded systems.
Key Features:
Uses a microprocessor as the CPU.
Has input, output, memory, and storage.
Designed for one user at a time.
Used in education, offices, homes, and small businesses.
Input Unit
Devices like keyboard, mouse, scanner.
Converts user data into a form understood by the microprocessor.
Central Processing Unit (CPU)
The microprocessor chip.
Controls all operations.
Performs arithmetic, logic, and control functions.
Memory Unit
Stores instructions and data.
Two types:
Primary memory (RAM, ROM)
Secondary storage (Hard disk, SSD)
Output Unit
Devices like monitor, printer, speakers.
Converts processed data into human-readable form.
✅ Exam Pointers (HSC)
Define microcomputer (2M).
Draw block diagram of a microcomputer (3M).
Explain any two components of a microcomputer (2–3M).
A generic microprocessor represents the basic structure and components that are common in almost all microprocessors.
It shows how instructions are fetched, decoded, and executed.
Every microprocessor, whether simple (8085) or advanced (Pentium), has these essential building blocks.
Arithmetic Logic Unit (ALU)
Performs all arithmetic (addition, subtraction, etc.) and logical operations (AND, OR, XOR, compare, etc.).
Works directly with data from registers or memory.
Registers
Small, high-speed storage inside the CPU.
Store temporary data, instructions, addresses, and intermediate results.
Types: General purpose registers, accumulator, program counter, stack pointer, flag register.
Program Counter (PC)
Holds the address of the next instruction to be executed.
Increments automatically after fetching each instruction.
Instruction Decoder
Interprets the binary instruction fetched from memory.
Sends control signals to other parts (ALU, registers, memory).
Timing and Control Unit
Generates control signals to synchronize all operations.
Coordinates between CPU, memory, and I/O devices.
Bus Buffers and Latches
Manage data flow inside the processor.
Ensure that signals/data are stable while being processed.
Internal Buses and Control Lines
Data bus – transfers actual data.
Address bus – carries memory/I/O addresses.
Control bus – carries control signals (Read/Write, etc.).
Control Inputs/Outputs
Handle external commands and communication.
Interrupt Control
Allows the CPU to pause current execution and service an urgent request (e.g., from keyboard or I/O device).
After servicing, CPU resumes the previous task.
The generic model helps students understand the core working principle of all microprocessors.
Once this is clear, it’s easy to study 8085, 8086, and modern CPUs.
✅ Exam Pointers (HSC):
Define generic microprocessor (2M).
Draw and label block diagram (3–4M).
Explain functions of ALU, PC, Decoder, Registers (4–6M).
Intel 8085 is an 8-bit microprocessor with a 40-pin Dual In-line Package (DIP).
It has 16-bit address bus, 8-bit data bus, and control signals.
Each pin has a specific function to communicate with memory, I/O devices, and external hardware.
Pins: 8 lines (A15–A8)
Used to carry the higher-order 8 bits of the 16-bit memory address.
Unidirectional (only from processor to memory/I/O).
Pins: 8 lines (AD7–AD0)
Dual purpose:
During T1 state → carries lower-order 8 bits of address (A7–A0).
During rest → works as data bus (D7–D0).
Bidirectional.
ALE (Address Latch Enable): Distinguishes between address & data on AD7–AD0.
RD̅ (Read): Active low signal to read from memory/I/O.
WR̅ (Write): Active low signal to write into memory/I/O.
IO/M̅: Distinguishes between I/O (1) and Memory (0).
S1, S0: Status signals (used internally).
Vcc (Pin 40): +5V supply.
Vss (Pin 20): Ground.
X1, X2 (Pins 1 & 2): Connected to crystal oscillator for system clock.
CLK (Clock Out): Provides clock signal for peripherals.
RESET IN: Resets program counter and flags.
RESET OUT: Indicates processor is resetting.
READY: Used to delay microprocessor until slow I/O/memory is ready.
HOLD: Indicates peripheral requesting control of buses.
HLDA (Hold Acknowledge): Acknowledgement for HOLD.
INTR (Interrupt Request): General interrupt.
INTA̅ (Interrupt Acknowledge): Acknowledges INTR.
RST 5.5, RST 6.5, RST 7.5: Maskable vectored interrupts.
TRAP: Non-maskable highest priority interrupt.
SID (Serial Input Data): Accepts serial data bit by bit.
SOD (Serial Output Data): Sends serial data bit by bit.
Draw neat labelled diagram of 8085 pin configuration (4–5 marks).
Explain groups of signals: Address bus, Data bus, Control, Interrupts, Serial I/O (4–6 marks).
Difference between RESET IN and RESET OUT often asked.
The functional block diagram of 8085 microprocessor shows all the internal functional units and how they are connected. The Intel 8085 is an 8-bit microprocessor with a 16-bit address bus, 8-bit data bus, and 74 instructions.
Here’s a breakdown of the functional blocks:
An 8-bit register used to store data temporarily.
It is part of the Arithmetic and Logic Unit (ALU).
Used as one operand and also holds the result of operations.
Performs arithmetic operations (ADD, SUB, INCREMENT, DECREMENT) and
logic operations (AND, OR, XOR, Compare).
Works in conjunction with the accumulator and temporary registers.
Six 8-bit registers.
They can be combined as register pairs:
BC, DE, HL (for 16-bit operations).
The HL pair is often used as a memory pointer.
A 16-bit register.
Holds the address of the next instruction to be executed.
Automatically incremented after fetching each instruction.
A 16-bit register.
Points to the top of the stack in memory.
Stack is used for subroutine calls, returns, and temporary storage.
Instruction Register holds the opcode of the current instruction.
Decoder interprets it and generates signals for execution.
Used internally by the microprocessor during execution.
Not accessible to the programmer.
Contains 5 flags:
Sign (S)
Zero (Z)
Auxiliary Carry (AC)
Parity (P)
Carry (CY)
Indicate the status of the result after ALU operations.
Generates control signals like RD, WR, ALE, IO/M.
Synchronizes operations of the microprocessor with the clock.
Handles hardware and software interrupts.
Provides 5 interrupt lines: TRAP, RST7.5, RST6.5, RST5.5, INTR.
Also has INTA (Interrupt Acknowledge) signal.
Provides SID (Serial Input Data) and SOD (Serial Output Data) pins.
Used for serial communication.
Address Buffer: Holds the higher-order address (A8–A15).
Address/Data Buffer (Multiplexed): Lower-order address (A0–A7) and data (D0–D7) are time-multiplexed.
Provides the necessary timing signals for synchronization.
8085 works with a clock frequency up to 3 MHz.
The Intel 8085 microprocessor supports several addressing modes, which define how the operand (data) of an instruction is specified.
Here are the addressing modes of 8085:
The operand (data) is given directly in the instruction.
Example:
Here, 32H is the immediate data.
The operand is in a register.
The instruction specifies the register name.
Example:
The memory address of the operand is given in the instruction.
Example:
Here, 2500H is the direct memory address.
The address of the operand is stored in a register pair (HL, BC, DE).
Example:
Here, the HL register pair holds the memory address.
The operand is implied in the instruction itself.
Example:
Here, the operand (Accumulator) is implied.