State any four features of USB serial communication protocol.
1 Answer

1.Multiple device connection: Upto 127 different devices can be connected on single USB bus.

2.Transfer rate: The initial USB supported 12 MBps transfer rate where USB 2.0 supports higher rate currently 60 MB/sec.

3.Support for large range of peripherals: Low bandwidth devices such as keyboard, mouse, joystick, and game -port, FDD . 4.Hub architecture: The devices are not daisy chained. Each device is connected to an USB hub. The USB hub interacts with PC on one side and peripheral on other side.

5.Plug ability: The USB device can be connected without powering off a PC i.e. plug and play feature in BIOS together with the device takes care of detection, handling and device recognition.

6.Power allocation: USB controller in the PC detects the presence or absence of the USB devices and does the allocation of power.

7.Ease of installation: There is only one cable. A 4-pin cable carries signals like power signal (-), signal (+), ground.

8.Host centric: The CPU software initiates every transaction on the USB bus. Hence the overhead on the PC increases when there are large number of peripherals involving large number of transactions.

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