Understand the USB interface and how it is used to transmit data
Types and Methods of Data Transmission 📡
Analog vs Digital: Think of analog as a continuous wave like a radio signal, while digital is like a series of on/off switches (0s and 1s). Digital is more reliable because it’s less affected by noise.
Serial vs Parallel: Parallel sends many bits at once (like a group of friends passing notes together). Serial sends one bit at a time (like a single line of text). Serial is simpler and faster over long distances.
Transmission Media 🚀
- Wired: copper, fiber‑optic, coaxial.
- Wireless: radio, infrared, Bluetooth, Wi‑Fi.
Speed & Bandwidth ⚡
Bandwidth is the maximum data rate. For example, $1 \text{ Gbps} = 1,000,000,000 \text{ bits/s}$.
USB Interface 🔌
USB (Universal Serial Bus) is a serial interface that uses a standard plug to connect devices. It’s like a universal phone charger that works with many gadgets.
USB Architecture 🏗️
- Host controller (your computer).
- Hub (optional, expands ports).
- Device (keyboard, mouse, phone, etc.).
USB Data Transfer Types 📦
- Control: configuration and status.
- Bulk: large data (e.g., file copy).
- Interrupt: small, time‑critical data (e.g., mouse movement).
- Isochronous: continuous data (e.g., audio/video).
USB Speed Classes 🚗
| Class | Max Speed | Typical Use |
|---|---|---|
| Low Speed | 1.5 Mbps | Mouse, keyboard |
| Full Speed | 12 Mbps | USB 1.1 devices |
| High Speed | 480 Mbps | USB 2.0 devices |
| SuperSpeed | 5 Gbps | USB 3.0 devices |
| SuperSpeed+ | 10 Gbps | USB 3.1 devices |
USB Pin Layout 🔌
USB uses a 4‑pin connector: VBUS (+5 V), D‑, D+, GND. Think of D+ and D‑ as two lanes of a road carrying the same traffic in opposite directions.
USB Power Delivery ⚡
USB can supply power: 5 V at 500 mA (USB 2.0), 900 mA (USB 3.0), and up to 20 V for USB Power Delivery (USB PD) devices.
Exam Tips for IGCSE 0478 💡
- Remember: Serial is one lane, Parallel is many lanes.
- USB is a serial interface, not parallel.
- Know the USB speed classes and typical devices for each.
- USB pin order: VBUS, D‑, D+, GND.
- Think of USB as a single lane highway that can carry many cars (bits) at once.
Revision
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