---
title: "PC interfacing techniques for I/O device"
subject: "Instrumentation II"
chapter: 2
key: "semester_5/instrumentation_ii:pc-interfacing-techniques"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/pc-interfacing-techniques
site: BCT Engineering
---

# PC interfacing techniques for I/O device

Instrumentation II · Chapter 2: Parallel Interfacing With Microprocessor Based System

- Asked in: 2074 Chaitra, 3 marks; 2070 Chaitra, 3 marks (asked 2 times)
- Video: [I/O Interface in Computer Organization](https://www.youtube.com/watch?v=PM728r4oGcE) — Gate Smashers
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/pc-interfacing-techniques
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-2

## Question

Describe various well-known techniques while interfacing an I/O device with a personal computer system.

## Short answer

Common I/O interfacing techniques include programmed (polled) I/O, interrupt-driven I/O using the 8259 PIC, DMA via the 8237 controller, memory-mapped and I/O-mapped access, bus-slot cards (ISA/PCI), and standard ports such as parallel, serial, and USB.

## Answer

Well-known techniques for interfacing an I/O device with a personal computer are:

1. **Programmed (polled) I/O:** the CPU reads the device status register and transfers data using IN/OUT instructions when ready. Simple but wastes CPU time.
2. **Interrupt driven I/O:** the device raises an IRQ (via the 8259 PIC); the CPU runs an ISR to transfer the data.
3. **DMA:** the 8237 DMA controller transfers blocks directly between device and memory.
4. **Memory mapped and I/O mapped access:** the device registers sit in the memory space or in the I/O port space (e.g. LPT at 378H, COM1 at 3F8H).
5. **Bus slot (expansion card) interface:** an interface card with address decoder and buffers on the ISA/PCI/PCIe bus.
6. **Standard port interfaces:** parallel (LPT/Centronics), serial (RS-232), USB, and wireless links.

The choice depends on the data rate, number of devices and available CPU time.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the drawback of programmed (polled) I/O?
   A. It wastes CPU time
   B. It needs DMA
   C. It cannot read status
   D. It needs an 8259
   Answer: A. The CPU keeps checking the status register. (Key point: Programmed I/O)

2. Which chip handles IRQs in a PC for interrupt driven I/O?
   A. 8259 PIC
   B. 8237
   C. 8255
   D. 8253
   Answer: A. The device raises an IRQ via the 8259 PIC. (Key point: Interrupt in PC)

3. Which are examples of I/O mapped port addresses in a PC?
   A. LPT at 3F8H and COM1 at 378H
   B. LPT at 378H and COM1 at 3F8H
   C. Both at 0000H
   D. Only memory addresses
   Answer: B. Those are standard PC port addresses. (Key point: Port addresses)

4. What decides the technique chosen?
   A. Colour of the card
   B. Only cost of cable
   C. Data rate, number of devices and available CPU time
   D. The monitor size
   Answer: C. These factors set the required performance. (Key point: Choice of technique)

## Related in Instrumentation II

- [PC based concrete purifying factory with 8255](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aconcrete-purifying-ppi-4000h) — Instrumentation II, chapter 2
- [Interfacing 8-bit ADC using interrupt](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aadc-interrupt-interface) — Instrumentation II, chapter 4, asked 2×
- [Interfacing: 512-byte RAM with 8085](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Arag-ram-512-interface) — Instrumentation II, chapter 2
- [USB 1.1 vs 2.0 and device identification](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ausb11-vs-usb20-identify) — Instrumentation II, chapter 3
- [8086 RAM/EPROM interfacing with reset address](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Arom-ram-8086-fffffh) — Instrumentation II, chapter 1
- [Digital transmission system; analog vs digital](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aanalog-digital-transmission-compare) — Instrumentation II, chapter 5

## Related in other subjects

- [Application, system and device domain](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Aapplication-system-device-domain) — Multimedia System, chapter 1
- [IP and soft switching for PC-to-PSTN calls](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aip-soft-switching-skype-pstn) — Telecommunications, chapter 8
- [Simulation of computer system serving WWW](https://www.bctengineer.com/question.md?key=semester_8%2Fsimulation_and_modeling%3Acomputer-system-www-request) — Simulation and Modeling, chapter 10, asked 2×
- [Continuous system simulation; analog computer example](https://www.bctengineer.com/question.md?key=semester_8%2Fsimulation_and_modeling%3Acontinuous-simulation-analog-example) — Simulation and Modeling, chapter 3