As technology has become increasingly more advanced, so have the data transfer protocols used to facilitate communication between different devices. USB (Universal Serial Bus) protocols are one of the most common and important data transfer protocols used today. Understanding the fundamentals of USB protocols is essential for those seeking to design and implement technology solutions that leverage this protocol.
For those looking to prepare for interviews related to USB protocols, it is important to have a fundamental understanding of the technology, as well as the ability to answer questions that probe your knowledge. To help those seeking to increase their understanding of USB protocols as well as prepare for potential interview questions, this blog post will look at some of the most common USB protocol interview questions.
USB Structure and working| Embedded Systems
When working with USB, it’s important to first consider the interface capabilities of your central processing unit (CPU) or microcontroller (MCU), as this device is fundamental for high-speed data transfer in your design. If you find that you need to transmit data from a CPU or MCU to a connected peripheral with a data rate greater than 10 Mbps, USB can be a great fit.
2: When your interface’s data link reliability is poor, how can you send data over a long distance?
Designing a system that uses high-speed signals for data transmission can be difficult, especially when there are so many available communication protocols. While many are ideal for high-speed signals, one in particular continues to grow in popularity – the USB. Often been associated with gaming, automotive head unit, and PC and notebook applications, the USB protocol has become a more general-purpose high-speed data protocol, connector and cable specification due to its support for multiple types of data transfers and high-power charging. Figure 1 shows the evolution of USB since its release in 1998.
The USB Type-C® protocol’s introduction has significantly increased USB’s adaptability. Systems can respond to various types of connections in a variety of ways thanks to USB Type-C’s ability to enable the development of peripherals that serve as USB hosts or USB devices. Additionally, USB Type-C active multiplexers that provide signal integrity compliance with the USB specification can aid in ensuring that the interface is configured correctly.
The USB includes devices called USB hubs that can turn one port into multiple ports with minimal effort. Four-port high-speed USB hubs such as the TUSB4041I, TUSB8041A and TUSB8042A can help increase the number of devices that can be used at once.
Clarification: Devices are given 7-bit addresses to facilitate identification.
6. USB transmits data in parallel, which allows for extremely quick data transfer rates. a) True b) False.
3. The sampling process in speaker output is a ________ process. Asynchronous, Synchronous, Isochronous, None of the Above, and Synchronous
Clarification of the response: This indicates that the USB receives both the data and the control signals necessary for the transfer operation.
8. By participating in _____ for the communication path, the device can communicate with the host and send a message. Arbitration, polling, prioritizing, or none of the above are possible.
How Does USB Transmit and Receive Data?
There are a number of mechanisms that must be followed, including how different USB devices should interact with one another upon enumeration and communication. How does the USB standard define how a USB cable or device should operate?
USB hosts, also referred to as master devices, are the ones who start all USB bus communication. Typically, a computer or other controller is regarded as the master, communicating with other devices only when they make specific requests for information. The host device is connected to the peripheral device, or slave device, which is programmed to give the host device the data it needs to function. Usb flash drives, computer mice, keyboards, cameras, and other similar devices are examples of typical peripheral devices.
It’s critical that host and peripheral devices can communicate with each other effectively. The ability of either one to carry out its job function will cause the communication between two devices to break down. For instance, if someone plugs a flash drive into their host computer and nothing happens, there may be a problem with the bus’s ability to communicate. which brings up how the USB bus facilitates communication Understanding the theory of operation behind how USB data is sent over the bus, the various USB data packet fields and packet types, and the various types of USB data transfers will help you comprehend how USB data is transmitted and received.
A USB packet is made up of discrete bits called USB data packet fields.
The fields in a USB data packet include the Sync field, the Packet ID (PID) field, the Address field, the Endpoint field, the CRC field, and the End of Packet (EOP) field.
Table 1: USB Packet Types
| PID Type | PID Name | Description |
| Token | OUT | Host to device transfer |
| IN | Device to Host transfer | |
| SOF | Start of Frame marker | |
| SETUP | Host to device control transfer | |
| Data | DATA0 | Data packet |
| DATA1 | Data packet | |
| DATA2 | High-Speed Data packet | |
| MDATA | Split/High-Speed Data packet | |
| Handshake | ACK | The data packet was received error free |
| NAK | Receiver cannot accept data or the transmitter could not send data | |
| STALL | Endpoint halted or control pipe request is not supported | |
| NYET | No response yet | |
| Special | PRE | Preamble to full-speed hub for low-speed traffic |
| ERR | Error handshake for Split Transaction | |
| SPLIT | Preamble to high-speed hub for low/full-speed traffic | |
| PING | High-speed flow control token | |
| EXT | Protocol extension token |
These fields are used to create data packets that specify the different transactions. There are four USB packet types including:
The host initiates a token packet, which decides whether the host will send or receive data.
Data packets are sent by the transmitter, and if a device is unable to respond, they can return a NAK or Stall packet.
Handshake Packet, used for acknowledging data or reporting errors.
The Start-of-Frame Packet schedules the data transfers by dividing the USB bus into time segments.
These frames are created from these packets and sent via a USB transaction. The transfer type being used for an endpoint determines the length and frequency of the transaction.
A specific endpoint on the device is the target of every communication between a USB host and a USB device. Each device endpoint is a unidirectional data sender or receiver, as well as a host-specific sender or receiver.
Each endpoint differs from the others in terms of bandwidth needs and data transfer methods. Control, isochronous, interrupt, and bulk transfers are the four different types of USB data transfers.
Control: Non-periodic transfers. Typically, used for device configuration, commands, and status operation.
Interrupt: This is a transaction that is promised to take place at a specific time. The device will specify how frequently the host should check the device to see if new data has arrived. This is used by keyboards and mice as input devices.
Isochronous: Periodic and continuous transfer for time-sensitive data. The data sent in these packets is not error-checked or retransmitted. Devices that require bandwidth reservations and have a high tolerance for errors use this. Examples include multimedia devices for audio and video.
Bulk: General transfer scheme for large amounts of data. This is for situations where it is more crucial that the data be transmitted accurately than for it to arrive promptly. Bulk transfers have the lowest priority. This transaction might take longer if there are a lot of transfers on the bus. The data is guaranteed to arrive without error. Data will be retransmitted if a CRC error is discovered. Files from a mass storage device or the output from a scanner are examples of this type of transfer.
An Introduction to the USB Protocol
In order to institutionalize a more widespread, uniform cable and connector that could be used across a variety of different devices, the USB protocol, also known as Universal Serial Bus, was first developed and introduced in 1996. Having a universal cable would help ease the confusion and inconvenience of having a collection of cables needed for each individual device as technological devices proliferate at this time.
The USB Implementors Forum, or USB-IF, is currently in charge of maintaining and regulating the USB architecture, which was developed with the help of a group of companies that included Compaq, Digital Equipment, IBM, Intel, Microsoft, and Northern Telecom. To be verified as a reliable USB source, USB device manufacturers must adhere to strict standards and specifications that are enforced by USB-IF. The USB logo notifies consumers and other USB adopters that cables or devices are safe to use when they are compliant with both the physical layer (mechanical and electrical) and software layer of the USB standard.
FAQ
How does USB protocol work?
USB device communication is done through pipes. These pipes serve as a conduit from the host controller to an endpoint, also known as an addressable buffer. An endpoint holds the data that is waiting to be transmitted to the host and stores the data that has been received from the host.
What are the USB protocols?
In order to institutionalize a more widespread, uniform cable and connector that could be used across a variety of different devices, the USB protocol, also known as Universal Serial Bus, was first developed and introduced in 1996.
What is the latest USB protocol?
USB 80 Gbps: The specification name is USB4 Version 2. 0 (released in October 2022). This revised specification improves the speed and data protocol performance of USB4, enabling product developers to create devices that can transfer data at up to 80 Gbps.
What are the features of the USB protocol?
The maximum number of peripherals that can be connected to one USB host controller is 127. The maximum speed of a USB device is 480 Mbps (for USB 2). 0). The maximum length of a single USB cable is 5 meters without a hub and 40 meters with a hub. USB acts as “plug and play” device.
