SAM7S256_14 Datasheet, PDF (505/775 Pages) ATMEL Corporation – ARM-based Flash MCU

35.5 Functional Description
35.5.1 USB V2.0 Full-speed Introduction
The USB V2.0 full-speed provides communication services between host and attached USB devices. Each device
is offered with a collection of communication flows (pipes) associated with each endpoint. Software on the host
communicates with a USB device through a set of communication flows.
Figure 35-3. Example of USB V2.0 Full-speed Communication Control
USB Host V2.0
Software Client
Data Flow: Control Transfer
Data Flow: Isochronous or Bulk In Transfer
Data Flow: Isochronous or Bulk Out Transfer
EP0
EP1 _{USB Device 2.0}
EP2
USB Device endpoint configuration requires that
in the first instance Control Transfer must be EP0.
The Control Transfer endpoint EP0 is always used when a USB device is first configured (USB v. 2.0 specifications).
35.5.1.1 USB V2.0 Full-speed Transfer Types
A communication flow is carried over one of four transfer types defined by the USB device.
Table 35-2. USB Communication Flow
Transfer
Direction
Bandwidth
Control
Bidirectional Not guaranteed
Isochronous
Unidirectional
Guaranteed
Interrupt
Unidirectional Not guaranteed
Bulk
Unidirectional Not guaranteed
Supported Endpoint Size
8, 16, 32, 64
64
≤64
8, 16, 32, 64
Error Detection
Yes
Yes
Yes
Yes
Retrying
Automatic
No
Yes
Yes
35.5.1.2 USB Bus Transactions
Each transfer results in one or more transactions over the USB bus. There are three kinds of transactions flowing
across the bus in packets:
1. Setup Transaction
2. Data IN Transaction
3. Data OUT Transaction
SAM7S Series [DATASHEET]
6175M–ATARM–26-Oct-12
505