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By PURPLELEC | 16 November 2023 | 0 Comments

How many devices can be linked to usb

  USB is a high-speed serial transmission bus that supports hot swapping. It uses differential signals to transmit data. The maximum speed of USB2.0 can reach 480Mb/S. USB supports two power supply modes: "bus powered" and "self-powered". In bus-powered mode, the device can draw up to 500mA.
  USB2.0 is designed to be backward compatible. When there are full-speed (USB 1.1) or low-speed (USB 1.0) devices connected to a high-speed (USB2.0) host, the host can support them through separate transmissions. On a USB bus, the highest transfer speed level that can be achieved is determined by the slowest "device" on the bus, which includes the host, HUB, and USB function devices.
USB system
  The USB system includes three parts: "host", "device" and "physical connection". The host is a complex of hardware, software and firmware that provides USB interface and interface management capabilities. It can be a PC or an OTG device. There is only one USB host in a USB system; the device includes USB functional devices and USB HUB. Supports up to 127 devices; the physical connection refers to the USB transmission line. In USB 2.0 systems, shielded twisted pair cable is required.
  A USB HOST can support up to 128 addresses at the same time. Address 0 is the default address and is only temporarily used during device enumeration and cannot be assigned to any device. Therefore, a USB HOST can support up to 127 addresses at the same time. If a device Occupying only one address, it can support up to 127 USB devices. In the actual USB system, if you want to connect 127 USB devices, you must use a USB HUB, and the USB HUB also needs to occupy an address, so the actual number of USB functional devices that can be supported will be less than 127.
  The USB system uses a layered star topology to connect all USB devices, as shown in the figure: starting from HOST-ROOT HUB, it supports layer 7 (Tier), which means that any USB system can allow up to 5 USBs. HUB cascade. A Compound Device will occupy two or more layers at the same time.
USB system
  Why up to 7 floors? Mainly limited by the hub and cable signal transmission time limitations.

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