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29.4
USB Function Operation
This chapter describes the basics of the USB function.
■ USB Function operation
The USB function performs a both way packet transfer with a host controller that supports the USB
protocol. A host PC and its devices are connected and configured by the enumeration process. Then,
communications based on various types of transfers using device drivers are performed.
This section describes the operation of the USB communications between a host PC and the USB device by
using enumeration as an example.
It illustrates the operations of registers and USB packets to understand the overview of USB
communication operation.
●
Enumeration process
It is the first communication process between a host PC and the USB devices before the USB can operate.
The host PC examines which devices are connected to the USB bus by using the USB Control transfer (one
USB transfer type). This uses the EP0 (endpoint0) out of six endpoints (as defined in the USB
specifications).
When EP1 to EP5 are used, the followings must be received on the USB bus.
1. USB bus reset.
2. Address set by SET_ADDRESS.
3. Configuration set by SET_CONFIG.
CHAPTER 29 USB FUNCTION
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