UPSD3422_06 Datasheet, PDF (148/293 Pages) STMicroelectronics – Turbo Plus Series Fast Turbo 8032 MCU with USB and Programmable Logic

USB interface
uPSD34xx
25.2.1
● Control Transfers (see Figure 53)
Control transfers are used to configure and send commands to a device. Control
transfers consist of two or three stages:
– SETUP
This stage always consists of a data packet with eight bytes of USB CONTROL
data.
– DATA stage (optional)
If the CONTROL data is such that the host is requesting information from the
device, the SETUP stage is followed by a DATA stage. In this case, the host sends
an IN token and the device responds with the requested data in the data packet.
– STATUS stage
This stage is essentially a handshake informing the device of a successfully
completed control operation.
Enumeration
Enumeration is the process that takes place when a device is first connected to the USB.
During enumeration, the host requests information from the device about what it is, how
many endpoints it has, the power requirements, bus bandwidth requirements, and what
driver to load. Once the enumeration process is complete, the device is available for use.
The enumeration process consists of a series of six steps as follows:
1. When a device is first connected to the USB, its address is zero. Upon detecting a new
device connected to the USB, the host sends a Get_Descriptor request to address
zero, endpoint0.
2. The device, upon receiving a Get_Descriptor request, sends data back to the host
identifying what it is.
3. The host resets the device and then sends a Set_Address request. This is a unique
address that identifies it from all other devices connected to the USB. This address
remains in effect until the device is disconnected from the USB.
4. The host sends more Get_Descriptor requests to the device to gather more detailed
information about it and then loads the specified driver.
5. The host will setup and enable the endpoints defined by the device.
6. The device is now configured and ready for use with the host communicating to the
device using the assigned address and endpoints.
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