৪৯তম বিসিএস ⎯ তথ্য ও যোগাযোগ প্রযুক্তি [২৮১]

A microprocessor is the central processing unit (CPU) of a computer system, implemented on a single chip. It performs computations, controls devices, and manages data processing. Due to its versatility and compactness, microprocessors are widely used in many applications, including the following,

Personal Computers and Laptops: Microprocessors form the core of PCs, laptops, and servers, executing all instructions and managing software applications.

Embedded Systems: Microprocessors are used in embedded systems to control devices like washing machines, microwaves, digital cameras, and smartphones.
They handle tasks like input/output operations, timing, and user interface management.

Robotics: Microprocessors control robotic arms, assembly lines, CNC machines, and other automated industrial systems.
They process sensor inputs, execute control algorithms, and manage communication between devices.

Source: Digital Logic and Computer Design by M. Morris Mano

A microprocessor is an integrated circuit that contains the CPU (Central Processing Unit) of a computer on a single chip. It performs arithmetic, logic, control, and input/output operations.

Example:
Intel 8085 and 8086 are examples of microprocessors that can execute instructions and control peripherals.

Source: Digital Logic and Computer Design by M. Morris Mano

A microprocessor typically consists of the following main components:

Arithmetic and Logic Unit (ALU):
• Performs arithmetic operations like addition, subtraction, multiplication, and division.
• Performs logical operations like AND, OR, NOT, XOR.

Registers:
• High-speed storage areas inside the microprocessor.
• Used to store data, instructions, addresses, or intermediate results.
• Types of registers:
(i) Accumulator (ACC): Stores intermediate results.
(ii) General Purpose Registers (B, C, D, E, H, L).
(iii) Program Counter (PC): Points to the next instruction to execute.
(iv) Stack Pointer (SP): Points to the top of the stack.
(v) Instruction Register (IR): Holds the current instruction.

Control Unit (CU):
• Directs the operation of the microprocessor.
• Decodes instructions and generates control signals.
• Coordinates data flow between ALU, registers, and input/output devices.

Bus Interface:
• Data Bus: Transfers data between the microprocessor and memory or I/O devices.
• Address Bus: Sends memory or I/O addresses from the CPU.
• Control Bus: Carries control signals like read/write.

Clock:
• Synchronizes all operations of the microprocessor.
• Determines the speed of instruction execution.

Source: Digital Logic and Computer Design by M. Morris Mano

The instruction set is a collection of commands the microprocessor can understand and execute, such as ADD, SUB, MOV, JMP. It is the interface between software and hardware.

Example:
Intel 8085 has instructions like MOV A,B (copy content of register B to A) and ADD B (add register B to accumulator A).

Source: Digital Logic and Computer Design by M. Morris Mano

1st generation: 4-bit or 8-bit processors, simple architecture, no microprogramming.
2nd generation: Introduced microprogramming to simplify instruction execution.
3rd generation: Integrated components like ALU and CU into single IC, e.g., Intel 8085.
4th generation: Introduced VLSI, RISC/CISC concepts, higher speed, and memory integration.

Source: Digital Logic and Computer Design by M. Morris Mano

• The address bus is a unidirectional bus used by the processor to specify the address of the memory location or I/O device that it wants to read from or write to.
• The processor puts an address on the address bus, this address tells which specific location in memory (RAM, ROM, cache) or which I/O device is being accessed.
• Data is then transferred to/from that location using the data bus.
• The control bus provides control signals (like Read/Write).

So, the address bus never carries data, only location (address information).

Example:
Suppose the processor wants to read data from memory location 2000H:
-> Processor places 2000H on the address bus.
-> Control bus sends a READ signal.
-> The memory at location 2000H places the data (e.g., 8A) on the data bus.
-> Processor reads the data 8A.
Here, the address bus only specified the location (2000H), not the data.

Source: Digital Logic and Computer Design by M. Morris Mano

The 8086 microprocessor is a 16-bit microprocessor with a 16-bit data bus and a 20-bit address bus. This allows the 8086 to access up to 1 MB of memory (since 2²⁰=1,048,576 memory locations).

Example:
The 16-bit data bus means the processor can read or write 16 bits of data at a time. The 20-bit address bus allows the processor to address up to 1MB of memory.

Source: Digital Logic and Computer Design by M. Morris Mano

The Intel 8086 microprocessor has a total of 40 pins.
These pins include power supply, clock, ground, control signals, data bus, address bus, and other input/output pins necessary for communication with peripheral devices and memory.

The 8086 is a 16-bit microprocessor with a 40-pin dual in-line package (DIP). Some of the important pins include:
Pins 1–16: Address bus (A0–A15)
Pins 17–18: Data bus (D0–D15)
Pins 19–20: Control signals
Pins 21–40: Power supply, clock, reset, ground, etc.

Source: Digital Logic and Computer Design by M. Morris Mano

The 8086 uses a segmented memory model where memory is divided into segments. These segments are including Code Segment (CS), Data Segment (DS), Stack Segment (SS), Extra Segment (ES).
Each segment is 64KB in size, and a segment register holds the base address of each segment. The 8086 uses 16-bit segment registers and adds the offset address to get the full 20-bit physical address.

Example:
If the CS register contains the value 2000H and the IP (Instruction Pointer) contains 0100H, the physical address will be 2000H * 10 + 0100H = 20100H.

Source: Digital Logic and Computer Design by M. Morris Mano

The 8086 microprocessor supports a variety of instructions, including arithmetic, logic, and control instructions. ADD is an arithmetic instruction used to add values in registers or memory locations.

Example:
The ADD instruction in the 8086 microprocessor performs the addition of two operands and stores the result in the destination operand.

Source: Digital Logic and Computer Design by M. Morris Mano

The 8086 microprocessor typically operates at clock speeds of 4 MHz, 8 MHz, or 10 MHz. 8 MHz was a common clock speed for many of the early 8086 systems.

Example:
A clock speed of 8 MHz means the microprocessor can execute 8 million cycles per second.

Source: Digital Logic and Computer Design by M. Morris Mano

The 8086 microprocessor supports several addressing modes, including,
Direct addressing: Directly accessing memory locations using a constant address.
Register indirect addressing: Using a register to hold the address of the operand.
Indexed addressing: Using an index register and an offset to access memory.

Example:
• Direct addressing: MOV AX, [1234H]
• Register indirect addressing: MOV AX, [BX]
• Indexed addressing: MOV AX, [SI+10H]

Source: Digital Logic and Computer Design by M. Morris Mano

The 8086 microprocessor uses a 20-bit address bus, which means it can address up to 1MB of memory. This is calculated as 2²⁰=1,048,576 bytes (or 1MB). The memory segmentation scheme allows access to this 1MB using 16-bit segments, with each segment capable of holding 64KB.

Example:
A program using the 8086 microprocessor can access memory addresses from 00000H to FFFFFH.

Source: Digital Logic and Computer Design by M. Morris Mano

The Extra Segment (ES) is typically used for string operations. For example, the MOVSB, MOVSW, LODSB, and STOSB instructions use the ES segment for string manipulation. It is an additional data segment available for certain operations.

Example:
In a string copy operation, the ES register is used to store the destination address while the DS register holds the source address.

Source: Digital Logic and Computer Design by M. Morris Mano

The 8086 FLAGS register is 16 bits wide and contains status flags and control flags.
Important status flags included are
Carry Flag (CF): Set when an arithmetic operation generates a carry/borrow.
Zero Flag (ZF): Set when the result of an operation is zero.
Sign Flag (SF): Reflects the sign of the result (1 = negative, 0 = positive).
Overflow Flag (OF): Indicates signed overflow.
Parity Flag (PF): Indicates even parity of result.
Auxiliary Carry Flag (AF): Used in BCD operations.

Control flags: Interrupt Enable Flag (IF), Direction Flag (DF), Trap Flag (TF)

So Carry Flag, Zero Flag, and Sign Flag are all definitely part of the register.

Example:
If AL = 05h and SUB AL, 05h:
Result = 00h
ZF = 1 (since result is zero)
CF = 0 (no borrow)
SF = 0 (positive)

If AL = FFh (-1 signed) and ADD AL, 01h:
Result = 00h
ZF = 1, CF = 1, SF = 0

So all these flags are actively used.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

In register addressing mode, the operand is a register. The instruction directly operates on the registers without accessing memory.
MOV AX, BX moves the contents of register BX into register AX.

Example:
MOV AX, BX: This moves the value in BX directly into AX.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

In relative addressing mode, the operand is a memory address computed relative to the current program counter (PC) or instruction pointer (IP).

Example:
JMP 50H: This instruction jumps to the address that is 50H bytes forward from the current instruction pointer.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

The RD (Read) pin is an active-low signal used to indicate that the 8086 microprocessor is performing a read operation from memory or I/O devices. When this pin is active (low), the 8086 reads data from the memory address specified by the address bus.
Example:
When the 8086 needs to read from memory, the RD pin is activated, allowing the data to be placed on the data bus.

Source: Digital Logic and Computer Design by M. Morris Mano

The IDIV (Signed Integer Division) instruction in the 8086 microprocessor is used to perform division of signed integers. It divides the accumulator (AX register) by a specified operand (such as a register or memory location) and stores the quotient and remainder in AX and DX respectively.
IDIV works with signed integers, which means it takes into account the sign of the numbers involved in the division.
The result of the division will be stored in:
• AX (for the quotient)
• DX (for the remainder)

Example:
If the AX register contains the dividend and the operand contains the divisor, the result of the signed division will be placed in AX (quotient) and DX (remainder).

Source: Digital Logic and Computer Design by M. Morris Mano

An assembler is a tool used in computer programming that translates assembly language into machine code (binary code) that the processor can execute. It is an essential part of low-level programming, as assembly language is a human-readable representation of machine instructions.

Example:
For the 8086 microprocessor, assembly code like MOV AX, BX would be converted into its corresponding machine code by the assembler, such as 89 D8.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

Assembler directives are special instructions that are not translated into machine code but are used to control the assembly process, allocate memory, or define data segments. The .DATA directive is used to define the data segment in an assembly program, indicating where the variables are stored.

Example:
.DATA tells the assembler that the following lines will contain data (such as variables), while .CODE indicates the start of the code segment.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

The symbol table is used by the assembler to map labels (such as variable names or instruction labels) to their corresponding addresses. During the first pass of the assembler, a symbol table is created, and it is used in the second pass to resolve addresses.

Example:
If an instruction MOV AX, [ARRAY] is encountered, the assembler uses the symbol table to find the memory address of ARRAY and replaces the label with the actual address in the machine code.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

The clock generator outputs a continuous pulse wave at a fixed frequency. This frequency is used to synchronize the operations of the microprocessor, ensuring all components in the system work in harmony with each other.

Example:
In the 8086 microprocessor, the clock generator produces a 5 MHz clock signal, which defines the execution speed of the processor.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

The bus controller plays a crucial role in timing the data transfer by generating the control signals (such as RD, WR, M/IO) at appropriate times. This synchronization ensures that data is correctly transferred between the microprocessor, memory, and peripherals.

Example:
The bus controller ensures that data is available on the data bus at the right time when a memory read or write operation is triggered.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

SRAM stands for Static Random-Access Memory.
Unlike DRAM (Dynamic RAM), which must be refreshed periodically to retain data, SRAM stores data in flip-flops and does not need refreshing as long as power is supplied.

Characteristics of SRAM:
i. Fast access time: faster than DRAM.
ii. Expensive: uses more transistors (typically 6 per bit).
iii. Volatile: loses data when power is turned off.
iv. Used in caches (L1, L2, L3) and small memory buffers inside microprocessors.

Example:
Cache memory in a processor is typically made of SRAM because it requires fast access to data.

Source: Digital Logic and Computer Design by M. Morris Mano

EEPROM is a type of non-volatile memory, which means it retains data even after the power is switched off. It is often used to store configuration data in embedded systems and other devices. Unlike SRAM, EEPROM does not lose data when the power supply is removed.

Example:
EEPROM is often used to store BIOS settings in computers, where data needs to be retained even after the system is powered off.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

The address lines are used to specify which memory location the microprocessor wants to read from or write to in the SRAM. The address lines carry the address to the SRAM, determining where the data should be read from or written to.

Example:
In a system with 4KB of SRAM, if the address lines are set to 0x0010, the microprocessor will access the memory location at 0x0010.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

Parallel I/O offers higher data transfer speeds because multiple bits are transmitted simultaneously across multiple data lines. This makes it more suitable for short-distance, high-speed communication compared to serial I/O, where bits are transferred one at a time over a single line.

Example:
A parallel bus used for communication between a computer's CPU and memory can transfer 16 or 32 bits at once, while serial communication would only transfer 1 bit at a time.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

Parallel I/O is often used in high-speed devices that require transferring large amounts of data at once, such as hard disk drives (HDDs). HDDs use parallel interfaces to connect to the system, allowing fast data transfers between the drive and the processor.

Example:
A hard disk drive (HDD) uses a parallel ATA (PATA) interface, which enables faster data transfer compared to serial connections.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

In programmed I/O (PIO), the CPU actively controls the data transfer process by checking the status of the I/O device and manually reading from or writing to the device's registers. This type of I/O does not involve interrupts, and the CPU has to wait until the I/O operation is completed.

Example:
The CPU checks the status of a printer and directly transfers data to it by writing to the printer's data register.

Source: Structured Computer Organization by Andrew S. Tanenbaum

In programmed I/O, the CPU is responsible for actively managing the I/O operation. This means that the CPU spends time waiting for the I/O device to be ready or to complete the operation, which reduces overall system efficiency. In contrast, interrupt-driven I/O allows the CPU to perform other tasks while waiting for I/O operations to complete, making it more efficient.

Example:
When a disk is being read by the CPU using PIO, the CPU continuously checks the device’s status, wasting valuable CPU cycles.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

• Programmed I/O (PIO): In this method, the CPU directly controls data transfer between memory and I/O devices by continuously checking device status (polling).
• Since the CPU must constantly check whether the device is ready, it wastes CPU cycles that could be used for other tasks.
• This results in higher CPU utilization and lower overall system efficiency, especially in multitasking or high-performance systems.

Example:
• Suppose a CPU is transferring data from a keyboard (slow device).
• With PIO, the CPU must repeatedly check if a key is pressed, wasting time.
• With interrupt-driven I/O, the CPU continues other work and only responds when an interrupt signals that data is ready.

Source: Structured Computer Organization by Andrew S. Tanenbaum

Programmed I/O (PIO) is often used for simpler devices that do not need continuous or high-speed data transfer. In these cases, the CPU can afford to poll the I/O device and manage the data transfer without negatively impacting system performance.

Example:
A keyboard or display often uses PIO, where the CPU checks the device’s status at regular intervals to transfer data.

Source: Digital Logic and Computer Design by M. Morris Mano

An A/D converter (also called an ADC) is used to convert continuous analog signals (such as sound or temperature readings) into a digital format that can be processed by a microprocessor or digital system. This allows the system to handle real-world analog inputs.

Example:
A thermometer sensor outputs an analog voltage, and an A/D converter converts this voltage into a digital value that can be processed by a microcontroller.

Source: Structured Computer Organization by Andrew S. Tanenbaum

The sample rate (also known as sampling frequency) refers to the number of times per second the A/D converter takes samples of the analog input signal. A higher sample rate leads to more accurate representations of rapidly changing signals.

Example:
An A/D converter with a sample rate of 1 kHz samples the analog signal 1000 times per second.

Source: Structured Computer Organization by Andrew S. Tanenbaum

The 8254 PIT is used in microprocessor systems to produce accurate time delays, generate square wave signals, and provide timing control for various processes. It has three independent 16-bit counters, which can be programmed in different modes for different applications.

Example:
A system may use the 8254 PIT to generate periodic interrupts every 10 ms for task scheduling.

Source: Structured Computer Organization by Andrew S. Tanenbaum

The 8254 PIT has three independent 16-bit counters labeled Counter 0, Counter 1, and Counter 2. Each counter can operate in one of six modes, allowing it to generate time delays, square waves, or event counting.

Example:
Counter 0 may generate interrupts for a system timer. Counter 1 may drive a speaker, and Counter 2 may be used for baud rate generation.

Source: Structured Computer Organization by Andrew S. Tanenbaum

The 8254 PIT has six modes:
Mode 0: Interrupt on Terminal Count
Mode 1: Hardware Retriggerable One-Shot
Mode 2: Rate Generator
Mode 3: Square Wave Generator
Mode 4: Software Triggered Strobe
Mode 5: Hardware Triggered Strobe

There is no Mode 6 in the standard 8254 PIT.

Source: Structured Computer Organization by Andrew S. Tanenbaum

The 8254 PIT is commonly used to generate periodic interrupts for the system timer, control event sequencing, generate sound frequencies, or provide baud rate timing in serial communication. It is not used for arithmetic or memory storage.

Example:
The PIT may generate an interrupt every 10 ms to update a clock or manage task scheduling in the OS.

Source: Structured Computer Organization by Andrew S. Tanenbaum

The Intel 8254 Programmable Interval Timer (PIT) has 16-bit counters. Since the data bus is only 8 bits wide, the counter data must be transferred in two 8-bit parts (low byte and high byte).

The 8254 PIT supports three types of data access as below,
Load low byte only:  Only the lower 8 bits of the counter are loaded.
Load high byte only: Only the upper 8 bits of the counter are loaded.
Load low byte, then high byte (both): Full 16-bit counter value is loaded in two steps.

This flexibility allows programmers to optimize based on whether an 8-bit or 16-bit count value is required.

Example: 
Suppose you want to load a 16-bit value 1234H into a counter:
• First, load the low byte (34H).
• Then, load the high byte (12H).
If you only needed a smaller value (e.g., less than 256), you could load only the low byte.

Source: Structured Computer Organization by Andrew S. Tanenbaum

In synchronous communication, the clock signal is shared between the transmitter and receiver, or the timing is derived from the data itself. This allows continuous transmission of multiple bytes without start/stop bits, making it suitable for high-speed data transfer.

Example:
Communication between a microprocessor and a serial EEPROM may use synchronous serial interface like SPI (Serial Peripheral Interface).

Source: Structured Computer Organization by Andrew S. Tanenbaum

Low-speed devices like keyboards and RS-232 serial ports typically use asynchronous communication. This is sufficient for the low data rate and simple wiring since start/stop bits frame each byte for reliable transfer.

Example:
A standard PC COM port (RS-232) sends ASCII characters framed with start and stop bits.

Source: Structured Computer Organization by Andrew S. Tanenbaum

RS-232 is a standard for serial communication between devices.
The type of cable commonly used to connect two RS-232 devices directly is a Null Modem Cable.
A null-modem cable is used to connect two DTE (Data Terminal Equipment) devices directly without a modem. In this cable, the transmit (TxD) and receive (RxD) lines are crossed so that each device can send and receive data properly.

Example:
Connecting two PCs using RS-232 without a modem requires a null-modem cable.

Source: Structured Computer Organization by Andrew S. Tanenbaum

The RS-232 standard specifies that reliable communication can be maintained up to 50 feet (≈15 meters) at low baud rates such as 9600 bps. Longer cables or higher speeds may require signal boosters or line drivers.

Example:
A serial connection between a PC and a modem in a building typically uses cables shorter than 15 meters.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

Pin 2 (TxD - Transmit Data): This pin is used by the DTE (such as a computer or terminal) to transmit data to the DCE (such as a modem or other communication device).
So, when the DTE needs to send data, it uses Pin 2 for transmitting the data.

Summary of Relevant Pins:
Pin 1: GND - Shield Ground.
Pin 2: TxD - Transmitted Data. Carries data from the Data Terminal to the Data Set.
Pin 3: RxD - Received Data. Carries data from the Data Set to the Data Terminal.
Pin 4: RTS - Request to Send. Data Terminal signals the Data Set to prepare for data transmission.
Pin 5: CTS - Clear to Send. Data Set to signals to the Data Terminal that it’s ready for receiving data.
Pin 6: DSR - Data Set Ready. DCE is ready to receive and send data.
Pin 7: GND - System Ground. Zero voltage reference.
Pin 8: CD - Carrier Detect. Data Set signals to the Data Terminal about the detected carrier of another device.
Pin 9: Reserved
Pin 10: Reserved
Pin 11: STF - Select Transmit Channel.
Pin 12: S.CD - Secondary Carrier Detect.
Pin 13: S.CTS - Secondary Clear to Send.
Pin 14: S.TXD - Secondary Transmit Data.
Pin 15: TCK - Transmission Signal Element Timing.
Pin 16: S.RXD - Secondary Receive Data.
Pin 17: RCK - Receiver Signal Element Timing.
Pin 18: LL - Local Loop Control.
Pin 19: S.RTS - Secondary Request to Send
Pin 20: DTR - Da Remote Loop Control.
Pin 22: RI - Ring Indicator. Data Set signals to the Data Terminal about a detected ringing condition.
Pin 23: DSR - Data Signal Rate Selector.
Pin 24: XCK - Transmit Signal Element Timing.
Pin 25: TI - Test Indicator.

Example:
When a PC powers on, it asserts DTR, signaling to the connected modem that it is ready to start data communication.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

When an interrupt occurs, the CPU temporarily stops executing the current instructions, saves the state of the program, and jumps to the interrupt service routine (ISR), a special function designed to handle the interrupt. After the ISR completes, the CPU restores the program's state and resumes normal execution.

Example:
If a timer interrupt occurs, the CPU will execute the ISR for the timer, then return to its original task after handling the interrupt.

Source: Structured Computer Organization by Andrew S. Tanenbaum

The 8259A PIC is designed to manage interrupts in a microprocessor system. It allows for the prioritization of multiple interrupt sources and provides a mechanism for handling maskable interrupts. The PIC facilitates the efficient management of interrupt requests (IRQ) by the CPU, ensuring that higher-priority interrupts are processed first.

Example:
The 8259A PIC is often used in systems with multiple interrupt sources (e.g., keyboard, printer) to prevent conflicts and ensure timely processing.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

he 8237 DMA controller has 4 channels, each of which can handle a different data transfer request. This allows the system to manage multiple DMA operations concurrently, which can improve overall system efficiency.

Example:
Channel 0 might be used for keyboard input, while Channel 1 is used for disk data transfer.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss

The device that can use DMA (Direct Memory Access) to transfer data directly to memory, without involving the CPU, is typically a peripheral device such as given below,
1. Disk Controllers (Hard Disk Drives, SSDs, etc.):
Disk controllers can transfer large amounts of data directly from a disk to memory using DMA, without involving the CPU. This is particularly useful for high-speed data transfer when reading or writing to storage devices.
2. Network Interface Cards (NICs):
NICs can use DMA to transfer data directly between the network and system memory, bypassing the CPU. This allows for faster networking and reduces the load on the CPU.
3. Sound Cards:
Audio devices like sound cards can use DMA to transfer audio data directly to or from memory, which is useful for real-time processing of sound data in multimedia applications.
4. Graphics Processing Units (GPUs):
GPUs can use DMA to transfer large blocks of graphical data directly to memory (such as textures, frame buffers, etc.) for rendering without involving the CPU.
5. Analog-to-Digital (ADC) and Digital-to-Analog (DAC) Converters:
ADC and DAC devices can use DMA to transfer data from the analog world (after conversion to digital data) directly to memory or vice versa.
6. Printers and Scanners:
Printers and scanners may use DMA for transferring data from memory to the device, or vice versa, when performing high-speed operations.

Source: Data Structures and Algorithm Analysis in C by Mark Allen Weiss