NEC switch User Manual page 137

(2) Data/handshake packet reception interrupt servicing
INTUSBRD occurrence
Planned packet
was received?
No
USB_MODE is
data stage OUT
reception?
Yes
Re-transmit data reception
reservation processing
RETI
CHAPTER 8 USB FUNCTION
Yes
No
Transition processing to
status stage OUT reception
USB_MODE is SETUP?
Yes
USB request processing
DATA/ACK reception
processing to ENDPOINT 0
User's Manual U12978EJ3V0UD
USB_MODE is
No
waiting for communication
request?
No
ACK reception processing
to ENDPOINT 1
Yes
137