Datasheet

212
XMEGA B [DATASHEET]
8291B–AVR–01/2013
Figure 18-4. OUT transaction.
The USB module then fetches the endpoint DATAPTR register and waits for a DATA0 or DATA1 packet. If a PID error or
any other PID than DATA0 or DATA1 is detected, the USB module returns to idle and waits for the next token packet.
If the STALL flag in the endpoint CTRL register is set, the incoming data are discarded. If the endpoint is not
isochronous, and the bit stuffing and CRC of the received data are OK, a STALL handshake is returned to the host, and
the STALL interrupt flag is set.
For isochronous endpoints, data from both a DATA0 and DATA1 packet will be accepted. For other endpoint types, the
PID is checked against TOGGLE. If they don't match, the incoming data are discarded and a NAK handshake is returned
to the host. If BUSNACK0 is set, the incoming data are discarded. The overflow flag (OVF) in the endpoint STATUS
register and the overflow interrupt flag (OVFIF) in the INTFLAGSASET/CLR register are set. If the endpoint is not
isochronous, a NAK handshake is returned to the host.
The incoming data are written to the data buffer pointed to by DATAPTR. If a bit-stuff error is detected in the incoming
data, the USB module returns to idle and waits for the next token packet. If the number of received data bytes exceeds
the maximum data payload specified by SIZE, the remaining received data bytes are discarded. The packet will still be
checked for bit-stuff and CRC errors. If there was a bit-stuff or CRC error in the packet, the USB module returns to idle
and waits for the next token packet.
If the endpoint is isochronous and there was a bit-stuff or CRC error in the incoming data, the number of received data
bytes, excluding CRC, is written to the endpoint CNT register. Finally, CRC and BUSNACK0 in the endpoint and
STATUS and CRCIF in INTFLAGSASET/CLR are set.
If data was successfully received, an ACK handshake is returned to the host if the endpoint is not isochronous, and the
number of received data bytes, excluding CRC, is written to CNT. If the number of received data bytes is the maximum
data payload specified by SIZE no CRC data are written in the data buffer. If the number of received data bytes is the
maximum data payload specified by SIZE minus one, only the first CRC data byte is written in the data buffer If the
number of received data bytes is equal or less than the data payload specified by SIZE minus two, the two CRC data
bytes are written in the data buffer.
Finally, the transaction complete flag (TRNCOMPL0) and BUSNACK0 are set and TOGGLE is toggled if the endpoint is
not isochronous. The transaction complete interrupt flag (TRNIF) in INTFLAGSBCLR/SET is set. The endpoint's
configuration table address is written to the FIFO if the transaction complete FIFO mode is enabled.
OUT
TOKEN
ADDRESS
ADDRESS
MATCH?
ENDPOINT
LEGAL
ENDPOINT?
EP STATUS
ENABLED?
PID PID OK?
DATA BIT STUFF
BIT STUFF
OK?
CRC OK? ACK
IDLE
oNoNoN
oNoN
STALL &
ISO?
STALL?
STALL
ISO? DATA
No
BUSNACK0
SET?
NAK
oN
seY
No
No
READ
CONFIG
UPDATE
STATUS
STORE
DATA
STORE
DATA
No
s
e
YseYseY
seY
Yes
Yes
Yes
READ
CONFIG
PIDO/1
OK?
NAK
UPDATE
STATUS
No
Yes
DATA
BIT STUFF CRC
BIT STUFF
OK?
CRC OK?
BUSNACK0
SET?
CRC
oNs
e
Y
Yes
Yes
No
Yes
No
Yes