Why this topic is important for ECET?
Interfacing is the bridge between microcontrollers and external devices like sensors, actuators, displays, and memory. Without proper interfacing, embedded systems cannot communicate with the real world.
In ECET 2026, questions on I/O ports, memory interfacing, buses, and protocols are expected – both conceptual and numerical. Mastering interfacing ensures you can handle practical problems and score quickly.
📘 Concept Notes
1. What is Interfacing?
Interfacing means connecting a microprocessor/microcontroller with external devices so that they can exchange data correctly.
Types of interfacing:
- I/O interfacing → For input/output devices (switches, LEDs, displays).
- Memory interfacing → For external RAM, ROM, or flash memory.
2. Memory Interfacing
- A microcontroller has a limited internal memory.
- External memory is added using address bus, data bus, and control signals.
- Address Bus: Selects memory location.
- Data Bus: Transfers data.
- Control Lines: Indicate read/write operations.
Example: If a microcontroller has 16 address lines → it can access:
3. I/O Interfacing
- For devices like LEDs, motors, and switches.
- Two modes:
- Memory-mapped I/O → I/O devices treated like memory.
- Isolated I/O (Port-mapped) → Separate instructions for I/O.
4. Peripheral Interfacing Examples
- LED Display: Port pin → current limiting resistor → LED.
- Seven Segment Display: Controlled using BCD-to-7 segment decoder (like 7447).
- Keyboards: Matrix arrangement interfaced using scanning technique.
- Motors: Stepper motors controlled by sending pulse sequences.
5. Serial & Parallel Interfacing
- Parallel: Many data bits transferred at once (fast but uses more pins).
- Serial: Data transferred bit by bit using protocols like UART, SPI, I²C (saves pins, widely used in embedded).
6. Interrupt vs Polling
- Polling: CPU continuously checks device status.
- Interrupt: Device signals CPU only when needed → more efficient.
⚙️ Formulas
- Memory locations accessed:
(where n = number of address lines) - Memory size in bytes:
Address range (hex):
Data transfer rate (serial):
🔟 10 MCQs
Q1. If a microcontroller has 12 address lines, the maximum memory it can address is:
a) 2 KB
b) 4 KB
c) 8 KB
d) 16 KB
Q2. Which technique treats I/O devices as memory locations?
a) Isolated I/O
b) Memory-mapped I/O
c) Serial I/O
d) Parallel I/O
Q3. A microcontroller uses 10 address lines and 8-bit data lines. Total accessible memory size is:
a) 512 bytes
b) 1024 bytes
c) 2 KB
d) 4 KB
Q4. In serial interfacing, UART stands for:
a) Universal Asynchronous Receiver Transmitter
b) Unified Asynchronous Register Transfer
c) Universal Address Register Transfer
d) None
Q5. In a 7-segment LED display, which IC is commonly used as BCD to 7-segment decoder?
a) 7483
b) 7447
c) 7485
d) 74138
Q6. Polling is less efficient than interrupts because:
a) It wastes CPU time
b) It needs more memory
c) It cannot detect inputs
d) It stops data transfer
Q7. For 16 address lines and 8 data lines, total memory size is:
a) 64 KB
b) 128 KB
c) 32 KB
d) 16 KB
Q8. Which of the following is a serial communication protocol?
a) SPI
b) I²C
c) UART
d) All of the above
Q9. If a system clock = 1 MHz and baud rate divisor = 16, the baud rate is:
a) 4800
b) 62500
c) 9600
d) 16000
Q10. Which one is NOT an interfacing device?
a) ADC
b) DAC
c) Op-Amp
d) ALU
✅ Answer Key
| Q No | Answer |
|---|---|
| Q1 | d |
| Q2 | b |
| Q3 | b |
| Q4 | a |
| Q5 | b |
| Q6 | a |
| Q7 | a |
| Q8 | d |
| Q9 | c |
| Q10 | d |
🧠 Explanations
- Q1: 12 lines →
× 1 byte = 4 KB. Correct = (d). - Q2: Memory-mapped I/O treats devices as memory → (b).
- Q3: 10 lines →
locations = 1024 bytes = 1 KB. Correct = (b). - Q4: UART → Universal Asynchronous Receiver Transmitter → (a).
- Q5: 7447 is BCD to 7-segment decoder → (b).
- Q6: Polling wastes CPU cycles → interrupts are efficient → (a).
- Q7: 16 lines →
locations × 1 byte = 64 KB → (a). - Q8: All three (SPI, I²C, UART) are serial → (d).
- Q9: Baud rate =
. Correct = (c). - Q10: ALU is processor’s internal block, not interfacing device → (d).
🎯 Motivation / Why Practice Matters
Interfacing basics form the foundation of Embedded Systems. In ECET 2026:
- Direct formula-based questions on memory size and address range appear.
- Conceptual questions on polling vs interrupts, I/O modes, UART/SPI/I²C are common.
- Practicing ensures accuracy under time pressure, and builds confidence for both ECET and higher exams like GATE.
📲 CTA
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