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CHAPTER 8 USB FUNCTION
User’s Manual U12978EJ3V0UD
151
8.8.5 Bit stuffing/strip controller operation
This circuit counts the number of “logic 1” of transmit/receive packets. If six successive logic 1s are detected, it
outputs an increment disable signal to the transmit/receive pointer (USBPOB). During packet transmission, it inserts
“logic 0” simultaneously with the increment disable signal.
Moreover, during bit stripping, if the bit that should be deleted was a “logic 1,” this is detected as a bit stuffing
error.
Figure 8-32. Timing of Bit Stuffing/Strip Controller Operation
(1) Bit stuffing
If “1” occurs six successive times, a “0” is inserted forcibly to shift the level.
Idle
NRZI
encoding data
Sync pattern Packet data
Idle
Bit stuffing
data
Sync pattern Packet data
Idle
RAW data
Sync pattern Packet data
Logic 1 × 6 times
Stuff bit
(2) Bit striping
If “1” occurs six successive times, the next bit is deleted as a stuffing bit.
Idle
Bit stuffing data
(NRZI decoding)
Sync pattern Packet data
Idle
Bit strip data
Sync pattern Packet data
Stuffing bit
Logic 1 × 6 times