Digital Logic Fundamentals: Number Systems and Circuits
Question 1 (Compulsory – Short Answers)
(a) What is a Number System?
A number system is a way of representing numbers using a set of symbols and a base (radix). Examples include:
- Decimal (base 10)
- Binary (base 2)
- Octal (base 8)
- Hexadecimal (base 16)
(b) Why Digital Computers use Binary Number System?
Digital computers use binary because:
- Electronic circuits have two states: ON (1) and OFF (0).
- Binary is reliable and easy to implement.
- It results in less error in data processing.
(c) Convert (1001.0010)₂ to Decimal
Integer part:
1001₂ = 1×2³ + 0×2² + 0×2¹ + 1×2⁰ = 8 + 0 + 0 + 1 = 9
Fractional part:
.0010₂ = 0×2⁻¹ + 0×2⁻² + 1×2⁻³ + 0×2⁻⁴ = 0 + 0 + 1/8 + 0 = 0.125
✅ Answer = 9.125
(d) Difference between Combinational & Sequential Circuits
| Combinational Circuits | Sequential Circuits |
|---|---|
| Output depends only on present input. | Output depends on present input + past state. |
| No memory element. | Has memory element (e.g., flip-flops). |
| Example: Adder. | Example: Flip-Flop. |
(e) What is Flip-Flop?
A flip-flop is a memory element that stores 1 bit of data. Types include: SR, JK, D, T Flip-Flop.
(f) What is Encoder?
An encoder converts multiple inputs into fewer outputs. Example: 8-to-3 encoder.
(g) What are SISO and PISO?
- SISO: Serial In Serial Out
- PISO: Parallel In Serial Out
Both are types of shift registers.
(h) What is ROM?
ROM (Read Only Memory) is a non-volatile memory used to store permanent data like BIOS.
Unit I Concepts (14 Marks)
Q. What are BCD Codes? Explain in detail.
BCD (Binary Coded Decimal) represents decimal digits using 4-bit binary numbers.
| Decimal Digit | BCD Code |
|---|---|
| 0 | 0000 |
| 1 | 0001 |
| 9 | 1001 |
Advantages:
- Easy decimal conversion.
- Widely used in calculators.
Disadvantages:
- Wastes memory (compared to pure binary).
- Arithmetic operations are more complex.
Unit II Concepts (14 Marks)
Q. What is K-Map? Simplify Boolean Expression using K-Map.
Karnaugh Map (K-Map) is a graphical method used to simplify Boolean expressions.
Simplification Steps:
- Plot the minterms (1s) on the map based on the expression.
- Make groups of 1, 2, 4, or 8 adjacent cells.
- Write the simplified expression based on the groups.
NAND Gate Realization:
- NAND is a universal gate.
- Any logic function can be built using only NAND gates.
Unit III Concepts (14 Marks)
Q. What are Sequential Circuits? Explain Shift Registers.
Sequential circuits depend on:
- Present input.
- Past output (memory state).
Shift Registers:
Shift registers are used for data transfer and storage, characterized by how data enters and exits:
- SISO (Serial In Serial Out)
- SIPO (Serial In Parallel Out)
- PISO (Parallel In Serial Out)
- PIPO (Parallel In Parallel Out)
Q. What are Counters? Explain types.
A counter is a sequential circuit that counts clock pulses.
Types of Counters:
- Asynchronous Counter (Ripple Counter)
- Synchronous Counter
- Up Counter
- Down Counter
- Mod-N Counter
Unit IV Concepts (14 Marks)
Q. What are I/O Devices? Explain their Controllers.
I/O Devices Categories:
- Input: Keyboard, Mouse.
- Output: Monitor, Printer.
- Storage: HDD, Pen Drive.
I/O Controller Function:
- Acts as an interface between the CPU and the peripheral device.
- Manages the flow and transfer of data.
- Handles device-specific signals and status reporting.
Q. What is Interrupt? Explain types with example.
An interrupt is a signal that temporarily stops the CPU’s current execution to handle a high-priority event.
Types of Interrupts:
- Hardware Interrupt – e.g., Keyboard input detected.
- Software Interrupt – e.g., System call execution.
- Maskable (can be ignored by CPU).
- Non-Maskable (must be serviced immediately).
Basic Interrupt Structure:
- Interrupt Request signal received.
- CPU saves its current state (context).
- Interrupt Service Routine (ISR) executes.
- CPU resumes the original program.
🎯 Exam Tip Summary
✔ Include Diagrams for full marks.
✔ Use clear Headings and relevant Examples.
✔ Write procedural steps clearly.
✔ Avoid lengthy, unnecessary descriptions.
अगर आप चाहो तो मैं:
- ✍️ Answer writing PDF
- 📒 Unit-wise short notes
- ❓ Expected questions for next exam
- 🧠 Easy memory tricks
बस बताओ 👍
ठीक है 👍
मैं 14 नंबर के हिसाब से, proper definition + headings + explanation + examples के साथ लिख रहा हूँ।
आप direct exam में ऐसे ही लिख सकते हो.
🔷 Q.8 What are I/O Devices? Explain their Controllers in detail. (14 Marks Answer)
🔹 Definition of I/O Devices
Input/Output (I/O) devices are hardware components that allow a computer system to communicate with the external world. These devices help the computer to receive data (input) and display or store results (output).
🔹 Types of I/O Devices
1️⃣ Input Devices
Input devices are used to enter data and instructions into the computer.
Examples:
- Keyboard
- Scanner
- Microphone
2️⃣ Output Devices
Output devices are used to display the processed result.
Examples:
- Monitor
- Printer
- Speaker
- Plotter
3️⃣ Storage Devices
These devices store data permanently or temporarily.
Examples:
- Hard Disk (HDD)
- Pen Drive (Flash Memory)
- CD/DVD
🔹 Role of I/O Controller
An I/O Controller (or Interface Unit) acts as the intermediary between the high-speed Central Processing Unit (CPU) and the relatively slow peripheral I/O devices.
Key Functions of I/O Controller:
- Buffering: It temporarily holds data to reconcile the speed mismatch between the CPU and the device.
- Status Reporting: It maintains the status of the device (ready, busy, error) and reports it to the CPU.
- Data Formatting: It converts data formats between the internal bus format (e.g., parallel) and the device-specific format (e.g., serial for a printer).
- Command Interpretation: It receives commands from the CPU (like READ or WRITE) and translates them into the necessary control signals for the device.
- Error Detection: It often includes logic to detect basic errors during data transfer.