SAM7X256_14 Datasheet, PDF (433/662 Pages) ATMEL Corporation – ARM-based Flash MCU

34.5.1.2 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
34.5.1.3 USB Transfer Event Definitions
As indicated below, transfers are sequential events carried out on the USB bus.
Table 34-3. USB Transfer Events
Control Transfers^{(1) (3)}
Interrupt IN Transfer
(device toward host)
Interrupt OUT Transfer
(host toward device)
Isochronous IN Transfer⁽²⁾
(device toward host)
Isochronous OUT Transfer⁽²⁾
(host toward device)
Bulk IN Transfer
(device toward host)
Bulk OUT Transfer
(host toward device)
 Setup transaction > Data IN transactions > Status
OUT transaction
 Setup transaction > Data OUT transactions > Status
IN transaction
 Setup transaction > Status IN transaction
 Data IN transaction > Data IN transaction
 Data OUT transaction > Data OUT transaction
 Data IN transaction > Data IN transaction
 Data OUT transaction > Data OUT transaction
 Data IN transaction > Data IN transaction
 Data OUT transaction > Data OUT transaction
Notes: 1. Control transfer must use endpoints with no ping-pong attributes.
2. Isochronous transfers must use endpoints with ping-pong attributes.
3. Control transfers can be aborted using a stall handshake.
A status transaction is a special type of host-to-device transaction used only in a control transfer. The control transfer
must be performed using endpoints with no ping-pong attributes. According to the control sequence (read or write), the
USB device sends or receives a status transaction.
SAM7X Series [DATASHEET]
6120K–ATARM–11-Feb-14
433