
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
-----
FNUM[10:8]
UDFNUMH
Read/Write
R
RRRRR
Initial Value
0
00000
Bit
76543210
FNUM[7:0]
UDFNUML
Read/Write
R
RRRRR
Initial Value
0
000000
Bit
7
6
5
4
3
2
1
0
-
FNCERR
-
UDMFN
Read/Write
R
R/W
R
Initial Value
0