28.3.2.5.2 Isochronous Endpoint

• The Underflow/Overflow Flag (UNFOVF) in endpoint STATUS and Underflow Interrupt Flag (UNF) in INTFLAGSA are set if the Data Buffer Not Acknowledge (BUSNAK) flag in endpoint STATUS or the Global NAK (GNAK) bit in the Control B (USB.CTRLB) register is set.

The data in the data buffer in SRAM pointed to by the Endpoint Data Pointer (EP[n].IN.DATAPTR) register are sent to the host in a DATA0 packet. When the number of data bytes specified in the CNT of the endpoint is sent, the CRC is appended and sent to the host.

BUSNACK and the Transaction Complete (TRNCOMPL) flag in the endpoint STATUS are set. TRNCOMPL in INTFLAGSB is set, and the endpoint address is written to the FIFO if this is enabled.