Datasheet

213
7799D–AVR–11/10
ATmega8U2/16U2/32U2
21.18.5 UDFNUMH – USB Device Frame Number High Register
• Bits 7:3 – Res: Reserved
These bits are reserved and will always read as zero.
• Bits 2:0 – FNUM[10:8]: Frame Number Upper Flag
These bits are read-only and updated by the hardware USB controller. These bits contains the 3
MSB of the 11-bits Frame Number information. The content of these bits is updated with the last
received SOF packet. These bits are updated even if a corrupted SOF has been received. When
a corrupted SOF number is detected, the FNCERR bit of UDMFN is set.
21.18.6 UDFNUML – USB Device Frame Number Low Register
• Bits 7:0 – FNUM: Frame Number Lower Flag
These bits are read-only and updated by the hardware USB controller. These bits contains the 8
LSB of the 11-bits Frame Number information. The content of these bits is updated with the last
received SOF packet. These bits are updated even if a corrupted SOF has been received. When
a corrupted SOF number is detected, the FNCERR bit of UDMFN is set.
21.18.7 UDMFN – USB Device Micro Frame Number
• Bit 7:5 – Res: Reserved
These bits are reserved and will always read as zero.
• Bit 4 – FNCERR: Frame Number CRC Error Flag
This bit is set by the USB controller when a corrupted frame number in Start of frame packet is
received. When an incorrect frame number is detected both SOFI flag and this bit are set.
• Bits 3:0 – Res: Reserved
These bits are reserved and will always read as zero.
Bit 76543210
(0xE5) ----- FNUM[10:8] UDFNUMH
Read/Write R R R RRRRR
Initial Value 0 0 0 00000
Bit 76543210
(0xE4) FNUM[7:0] UDFNUML
Read/Write R R R RRRRR
Initial Value 0 0 000000
Bit 7 6 5 4 3 2 1 0
(0xE6) - - - FNCERR - - - - UDMFN
Read/Write R R R R/W R R R R
Initial Value 0 0 0 0 0 0 0 0