ST STM32F102 Series Reference Manual page 488

USB full speed device interface (USB)
USB frame number register (USB_FNR)
Address offset: 0x48
Reset value: 0x0XXX where X is undefined
15 14 13
RXDP RXDM LCK
r r r
Bit 15 RXDP: Receive Data + Line Status
This bit can be used to observe the status of received data plus upstream port data line. It can be
used during end-of-suspend routines to help determining the wakeup event.
Bit 14 RXDM: Receive Data - Line Status
This bit can be used to observe the status of received data minus upstream port data line. It can be
used during end-of-suspend routines to help determining the wakeup event.
Bit 13 LCK: Locked
This bit is set by the hardware when at least two consecutive SOF packets have been received after
the end of an USB reset condition or after the end of an USB resume sequence. Once locked, the
frame timer remains in this state until an USB reset or USB suspend event occurs.
Bits 12:11 LSOF[1:0]: Lost SOF
These bits are written by the hardware when an ESOF interrupt is generated, counting the number
of consecutive SOF packets lost. At the reception of an SOF packet, these bits are cleared.
Bits 10:0 FN[10:0]: Frame Number
This bit field contains the 11-bits frame number contained in the last received SOF packet. The
frame number is incremented for every frame sent by the host and it is useful for Isochronous
transfers. This bit field is updated on the generation of an SOF interrupt.
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12 11 10 9
LSOF[1:0]
r r r r
8 7 6 5
FN[10:0]
r r r r
4 3 2 1
r r r r
RM0008
0
r