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UPSD3422 Datasheet(PDF) 155 Page - STMicroelectronics |
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UPSD3422 Datasheet(HTML) 155 Page - STMicroelectronics |
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155 / 300 page  Obsolete Product(s) - Obsolete Product(s) Obsolete Product(s) - Obsolete Product(s) UPSD3422, UPSD3433, UPSD3434, UPSD3454 USB interface 155/300 Figure 51. Interrupt transfer ● Control Transfers (see Figure 52) 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. 25.2.1 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. Token packet Data packet Handshake packet IN ADDR ENDP CRC5 CRC16 ACK Data1 Payload data AI10491b Obsolete Product(s) - Obsolete Product(s) |
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