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Section 20 USB Function Module
Rev. 4.00 Sep. 14, 2005 Page 773 of 982
REJ09B0023-0400
Status Stage (Control-OUT): The control-OUT status stage starts with an IN token from the
host. When an IN token is received at the start of the status stage, there is not yet any data in the
EP0iFIFO, and so an EP0i transfer request interrupt is generated. The application recognizes from
this interrupt that the status stage has started. Next, in order to transmit 0-byte data to the host, 1 is
written to the EP0i packet enable bit but no data is written to the EP0i FIFO. As a result, the next
IN token causes 0-byte data to be transmitted to the host, and control transfer ends.
After the application has finished all processing relating to the data stage, 1 should be written to
the EP0i packet enable bit.
USB function
Application
IN token reception
0-byte transmission to host
End of control transfer
Set EP0i transmission
complete flag
(USBIFR0/EP0i TS = 1)
Clear EP0i transfer
request flag
(USBIFR0/EP0i TR = 0)
Write 1 to EP0i packet
enable bit
(USBTRG/EP0i PKTE = 1)
Clear EP0i transmission
complete flag
(USBIFR0/EP0i TS = 0)
End of control transfer
Valid data
in EP0i FIFO?
ACK
Yes
No
NACK
Interrupt request
Interrupt request
Figure 20.9 Status Stage (Control-OUT) Operation