ATMEGA8U2_14 Datasheet, PDF (219/310 Pages) ATMEL Corporation – 125 Powerful Instructions – Most Single Clock Cycle Execution

ATmega8U2/16U2/32U2
21.18.15 UEINTX – USB Endpoint Interrupt Register
Bit
(0xE8)
Read/Write
Initial Value
7
FIFOCON
R/W
0
6
NAKINI
R/W
0
5
RWAL
R/W
0
4
NAKOUTI
R/W
0
3
RXSTPI
R/W
0
2
RXOUTI
R/W
0
1
STALLEDI
R/W
0
0
TXINI
R/W
0
UEINTX
• Bit 7 – FIFOCON: FIFO Control Bit
This bit can only be written to zero by software. Writing this bit to one has no effect. The behav-
ior of this bit depends on the direction of the selected endpoint.
• For OUT or CONTROL Endpoints:
This flag is set by the USB controller when a new OUT message is stored in the current bank. In
this situation RXOUT or RXSTP flags are also updated at the same time. Writing this bit to zero
frees the current bank and switches to the next bank.
• For IN Endpoints:
This flag is set by the USB controller when the current bank is free and can be loaded with new
data bytes. In this situation TXIN flag is also updated at the same time. Writing this bit to zero
sends the FIFO content and to switch the next bank.
• Bit 6 – NAKINI: NAK IN Received Interrupt Flag
This flag is set when a NAK handshake has been sent in response to a IN request from the host.
This NAKINI flag can generate a “USB endpoint interrupt” if NAKINE bit is set. Writing this bit to
zero acknowledges the interrupt source (USB clocks must be enabled before). Writing this bit to
one has no effect.
• Bit 5 – RWAL: Read/Write Allowed Flag
This flag is set by the USB controller and is relevant for all endpoint types except control end-
point. For an IN endpoint, this flag is set when the current bank is not full i.e. the firmware can
push at least one more byte into the FIFO (UPDATx register). For an OUT endpoint, this flag is
set when the current bank is not empty i.e. the firmware can read from the FIFO (UPDATx regis-
ter). When the STALLRQ bit is set or one of the endpoint error is set, this flag can not be set.
• Bit 4 – NAKOUTI: NAK OUT Received Interrupt Flag
This flag is set by the USB controller when a NAK handshake has been sent in response of a
OUT request from the host. This NAKOUTI flag can generate a “USB endpoint interrupt” if
NAKOUTE bit is set. Writing this bit to zero acknowledges the interrupt source (USB clocks must
be enabled before). Writing this bit to one has no effect.
• Bit 3 – RXSTPI: Received SETUP Interrupt Flag
This flag is set by the USB controller when a new valid (error free) SETUP packet has been
received from the host. This RXSTPI flag can generate a “USB endpoint interrupt” if RXSTPE bit
is set. Writing this bit to zero acknowledges the interrupt source (USB clocks must be enabled
before). Writing this bit to one has no effect.
• Bit 2 – RXOUTI / KILLBK: Received OUT Data Interrupt Flag
Depending on the direction of the endpoint, this bit has two functions:
• Endpoint OUT direction (RXOUTI flag):
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