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Section 20 USB Function Module
Rev. 4.00 Sep. 14, 2005 Page 778 of 982
REJ09B0023-0400
20.4.6 EP3 Interrupt-IN Transfer
USB function
Application
IN token reception
Data transmission to host
Set EP3 transmission
complete flag
(USBIFR1/EP3 TS = 1)
Write data to USBEP3 data
register (USBEPDR3)
Write 1 to EP3 packet
enable bit
(USBTRG/EP3 PKTE = 1)
Clear EP3 transmission
complete flag
(USBIFR1/EP3 TS = 0)
Write data to USBEP3 data
register (USBEPDR3)
Write 1 to EP3 packet
enable bit
(USBTRG/EP3 PKTE = 1)
Valid data
in EP3 FIFO?
Is there data
for transmission
to host?
Is there data
for transmission
to host?
No
Yes
No
Yes
No
Yes
NACK
ACK
Note: This flowchart shows just one example of interrupt transfer processing. Other possibilities include an
operation flow in which, if there is data to be transferred, the EP3 DE bit in the USB data status register
is referenced to confirm that the FIFO is empty, and then data is written to the FIFO.
Interrupt request
Figure 20.12 EP3 Interrupt-IN Transfer Operation