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 Flag (BUSNAK) 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 endpoint’s CNT is sent, the CRC is appended and sent to the host.

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