Datasheet

285
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
• Bits 7:5 - Reserved
The value read from these bits is always 0. Do not set these bits.
• Bit 4 - FNCERR -Frame Number CRC Error Flag
Set by hardware when a corrupted Frame Number in start of frame packet is received.
This bit and the SOFI interrupt are updated at the same time.
• Bits 3:0 - Reserved
The value read from these bits is always 0. Do not set these bits.
22.18.2 USB Device Endpoint Registers
• Bits 7:3 - Reserved
The value read from these bits is always 0. Do not set these bits.
• Bits 2-0 - EPNUM2:0 Endpoint Number Bits
Load by software to select the number of the endpoint which shall be accessed by the CPU. See “Endpoint
Reset” on page 270 for more details.
EPNUM = 111b is forbidden
• Bit 7 - Reserved
The value read from these bits is always 0. Do not set these bits.
• Bits 6-0 - EPRST6:0 - Endpoint FIFO Reset Bits
Set to reset the selected endpoint FIFO prior to any other operation, upon hardware reset or when an USB bus
reset has been received. See “Endpoint Reset” on page 270 for more information
Then, clear by software to complete the reset operation and start using the endpoint.
Bit 76543210
---FNCERR----UDMFN
Read/Wri
te
R
Initial
Value
00000000
Bit 76543210
- - - - - EPNUM2:0 UENUM
Read/Write R R R R R R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0
Bit 76543210
- EPRST6 EPRST5 EPRST4 EPRST3 EPRST2 EPRST1 EPRST0 UERST
Read/Write R R/W R/W R/W R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0