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With a host controller you will be able to communicate with all USB devices, and with a USB device controller you can just communicate with a host controller. USB host is the USB on the PC side in most cases and USB Device is the USB in your mouse ,keyboard, flash memory and so on.
USB has two different kinds of endpoint (connected device), like a client-server interface. One device is the computer (or host), and it's in charge: it's the server. All the other devices (the peripherals) are the clients, and can only communicate with the server.
You can't connect a host to a host, nor a peripheral to a peripheral. This distinction has historically been enforced by the connectors: hosts have type-A sockets, and peripherals have type-A plugs or type-B sockets. USB-C, however, uses the same connector for both hosts and peripherals.
Android supports a variety of USB peripherals and Android USB accessories (hardware that implements the Android accessory protocol) through two modes: USB accessory and USB host. In USB accessory mode, the external USB hardware acts as the USB host.
What is the difference between a host, embedded host, limited host and mini-host? Hosts are almost always referred to in a PC or laptop context, where any USB peripheral can be plugged into a USB port.
USB On-the-Go (OTG) allows two USB devices to talk to each other without requiring the services of a personal computer. Although OTG appears to add \"peer to peer\" connections to USB, it does not. Instead, USB OTG retains the standard USB host/peripheral model, where a single host talks to USB peripherals.
The answer to this requirement is in a developing standard called USB OTG (USB On-The-Go), a supplement to the USB specification that eliminates the requirement for a PC to act as host in exchanges of data among connected devices.
There is usually a lot of confusion between USB host and USB client. USB host is the system that connects to multiple USB clients. For example, the PC is a USB host and it can connect to multiple USB clients like mice, keyboards, and mass storage devices.
The answer to this requirement is in a developing standard called USB OTG (USB On-The-Go), a supplement to the USB specification that eliminates the requirement for a PC to act as host in exchanges of data among connected devices.
A 2.0 device always acts as a device and a 2.0 host always operates as a host. USB On-the-Go (OTG) and USB v3.0 (and above) provide the ability for a node to change roles from an upstream-facing port (device) to a downstream-facing device (host) and vice versa.
Since USB is a host-centric protocol, this distinction is quite important. So four combination of roles are possible. Type-C basic (DC-based) communication functionality (over CC pulls up-down) defines only the default swap function - either a host (and a power source), or a device (and a power sink).
A device that can serve as a “master” USB device, to which other “client” peripherals can be attached, is referred to as a “USB host.” Computers are USB hosts by default. Some other devices can also serve as USB hosts or can be switched to a “USB host mode” that allows them to serve as a connection point for peripherals. An ...
A host device is a computing device into which you can plug a peripheral. Some micros can be either a host or a peripheral. Using the mouse as an example: If your micro is emulating a mouse and plugged into a computer, it is a peripheral.
USB is a polled bus, where the USB Host initiates all data exchanges. The data travels to or from Endpoints in an USB Device. The client in the USB Host stores data in buffers, but does not have endpoints.
How USB Communicates. All USB data transfers are initiated by the USB host. The host controls communication timing by maintaining time intervals called frames. The host issues a Start of Frame (SOF) sequence on the USB data lines at the beginning of each frame.
There are two basic ways the hardware can provide the device mode functionality: with a separate "client port", which only supports the device mode, and with a USB OTG port, which can provide both device and host mode.
As far as the general case goes, Wikipedia is pretty explicit: "Use of USB On-The-Go allows those devices to switch back and forth between the roles of host and client devices". The official usb website, usb.org, has similar (but more verbose) language in its OTG section.
When your Android-powered device is in USB host mode, it acts as the USB host, powers the bus, and enumerates connected USB devices. USB host mode is supported in Android 3.1 and higher.
I think you should be able to detect it quite reliably by knowing the electrical properties of the pins. USB hosts pull the DP and DN data lines low with 15kOhm resistance. USB devices pull the DP line (DN line if it's a slow speed device) to 3 volts with a 1.5K resistance.
Don't know the difference between USB-A or USB-B? How about USB 4 and USB-C? Here are the USB standards and the devices that use them.