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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

1 2 ... 146 147 148 149 150 151 152 153 154 155 156 ... 233 234

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