1. VBUS (Power): This wire carries electrical power from the USB host to the connected device. The voltage level on this wire is usually +5 volts, providing power to the device's internal circuitry.
2. D+ (Data Plus): This wire is used for differential data transmission. It carries data signals from the host to the device or vice versa. The differential signaling method allows for reliable data transfer by comparing the voltage levels of D+ and D- wires to determine the data bits.
3. D- (Data Minus): This wire is used for differential data transmission. It complements the D+ wire, and the data signals transmitted through these two wires are used together to form the actual data being transferred.
4. Ground (GND): This wire provides a common ground connection between the host and the device. It ensures that both devices share the same electrical reference point, which is essential for proper electrical communication.
When you connect a USB device to a computer, the following process occurs:
1. Power Negotiation: The USB device initially draws power from the USB host through the VBUS wire. The host senses this power draw and determines the amount of power required by the device.
2. Device Enumeration: The host then begins the device enumeration process to identify and recognize the connected device. It involves exchanging control and configuration messages between the host and the device over the D+ and D- wires.
3. Data Transfer: Once the device is enumerated and configured successfully, data transfer can begin. Data is sent and received between the host and the device using the D+ and D- wires, following the USB communication protocol.
4. USB Bus Management: The USB connection is managed by the USB host, which controls and allocates bandwidth, power, and data flow between multiple connected devices.
It's important to note that there are different types of USB cables, with each type supporting different data transfer rates and power delivery capabilities. Common USB cable types include USB 2.0 (speeds up to 480 Mbps), USB 3.0 (speeds up to 5 Gbps), and the latest USB Type-C connector with varied data and power capabilities.
Overall, USB cables facilitate the communication and power exchange between devices and USB hosts, enabling the connection of a wide range of USB peripherals, from external storage drives to keyboards, printers, and smartphones, to computers and other devices.