Datasheet

228
XMEGA B [DATASHEET]
8291B–AVR–01/2013
18.14 Register Description – USB Endpoint
Each of the 16 endpoint addresses have one input and one output endpoint. Each endpoint has eight bytes of
configuration/status data located in internal SRAM.
The address to the first configuration byte is (EPPTR[15:0] + 16 × endpoint address) for output endpoints and
(EPPTR[15:0] + 16 × endpoint address + 8) for input endpoints.
Some bit locations have different functions, depending on endpoint configuration type or direction, and this is reflected by
using two different names for the bit locations.
18.14.1 STATUS – Status register
Note: 1. For isochronous endpoints.
 Bit 7 – STALL: STALL Flag
This flag is set when an IN or OUT transaction has been responded to with a STALL handshake. This flag is cleared by
writing a one to its bit location.
 Bit 7 – CRC: CRC Error Flag
This flag is set for isochronous output endpoints when a CRC error has been detected in an incoming data packet. This
flag is cleared by writing a one to its bit location.
 Bit 6 – UNF/OVF: Underflow/Overflow Flag
UNF: For input endpoints, the UNF flag is set when an input endpoint is not ready to send data to the host in response of
an IN token.
OVF: For output endpoints, the OVF flag is set when an output endpoint is not ready to accept data from the host
following an OUT token.
 Bit 5 – TRNCOMPL0: Transaction Complete Flag
This flag is set when an IN or OUT transaction has completed successfully. This flag is cleared by writing a one to its bit
location.
 Bit 4 – SETUP: SETUP Transaction Complete Flag
This flag is set when a SETUP, IN, or OUT transaction has completed successfully. This flag is cleared by writing a one
to its bit location.
 Bit 4 – TRNCOMPL1: Transaction Complete Flag
This flag is set when a SETUP, IN, or OUT transaction has completed successfully. This flag is cleared by writing a one
to its bit location.
 Bit 3 – BANK: Bank Select Flag
When ping-pong mode is enabled, this bit indicates which bank will be used for the next transaction. BANK is toggled
each time a transaction has completed successfully. This bit is not sed when ping-pong is disabled. This flag is cleared
by writing a one to its bit location.
 Bit 2 – BUSNACK1: Data Buffer 1 Not Acknowledge Flag
When this flag is set, the USB module will discard incoming data to data buffer 1 in an OUT transaction, and will not
return any data from data buffer 1 in an IN transaction. For control, bulk, and interrupt endpoints, a NAK handshake is
returned. This flag is cleared by writing a one to its bit location.
Bit 7 6 5 4 3 2 1 0
+0x00
STALL
UNF/ OVF TRNCOMPL0
SETUP
BANK BUSNACK1 BUSNACK0 TOGGLE
CRC
(1)
TRNCOMPL1
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0