Datasheet

Section 14 Universal Serial Bus (USB)
Rev.7.00 Dec. 24, 2008 Page 512 of 698
REJ09B0074-0700
14.5.5 Interrupt-In Transfer (Endpoint 3)
USB function Firmware
Receive IN token
Transmit data to host
Set EP3 transmit
complete flag
(EP3TS in UIFR0 = 1)
Write data to USB endpoint
data register 3 (UEDR3)
Write 1 to EP3 packet
enable bit
(EP3PKTE in UTRG0 = 1)
Clear EP3 transmit
complete flag
(EP3TS in UIFR0 = 0)
Write data to USB endpoint
data register3 (UEDR3)
Write 1 to EP3 packet
enable bit
(EP3PKTE in UTRG0 = 1)
Valid data
in EP3 FIFO?
Is there
transmit data
to host?
Is there
transmit data
to host?
No
Yes
No
Yes
No
Yes
NAK
ACK
Note: This flowchart shows just one example of interrupt-in transfer processing. Other possibilities include an
operation flow in which, if there is data to be transmited, the EP3DE bit UDSR is referred to confirm that the
FIFO is empty, and then data is written to the FIFO.
EXIRQx
Figure 14.17 EP3 Interrupt-In Transfer Operation