SN8F2250B Series
USB 2.0 Full-Speed 8-Bit Micro-Controller
9.4 USB ENUMERATION
A typical USB enumeration sequence is shown below.
1. The host computer sends a SETUP packet followed by a DATA packet to USB address 0 requesting the Device
descriptor.
2. Firmware decodes the request and retrieves its Device descriptor from the program memory tables.
3. The host computer performs a control read sequence and Firmware responds by sending the Device descriptor
over the USB bus, via the on-chip FIFO.
4. After receiving the descriptor, the host sends a SETUP packet followed by a DATA packet to address 0 assigning a
new USB address to the device.
5. Firmware stores the new address in its USB Device Address Register after the no-data control sequence
completes.
6. The host sends a request for the Device descriptor using the new USB address.
7. Firmware decodes the request and retrieves the Device descriptor from program memory tables.
8. The host performs a control read sequence and Firmware responds by sending its Device descriptor over the USB
bus.
9. The host generates control reads from the device to request the Configuration and Report descriptors.
10. Once the device receives a Set Configuration request, its functions may now be used.
11. Firmware should take appropriate action for Endpoint 0~3 transactions, which may occur from this point.
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