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Section 20 USB Function Module
Rev. 4.00 Sep. 14, 2005 Page 774 of 982
REJ09B0023-0400
20.4.4 EP1 Bulk-OUT Transfer (Dual FIFOs)
EP1 has two 64-byte FIFOs, but the user can perform data reception and receive data reads
without being aware of this dual-FIFO configuration.
When one FIFO is full after reception is completed, the USBIFR0/EP1 FULL bit is set. After the
first receive operation into one of the FIFOs when both FIFOs are empty, the other FIFO is empty,
and so the next packet can be received immediately. When both FIFOs are full, NACK is returned
to the host automatically. When reading of the receive data is completed following data reception,
1 is written to the USBTRG/EP1 RDFN bit. This operation empties the FIFO that has just been
read, and makes it ready to receive the next packet.