9990200011

Data Flow Types basie typesof data transfers

• Control Transfers:

Used to configure a device at attach time and can be used for other device-specific purposes, including control of other pipes on the device.

■    Bulk Data Transfers:

Generated or consumed in relatively large and burstyquantities and have wide dynamie latitude in transmission constraints.

■    Interrupt Data Transfers:

Used for characters or coordinates with human-perceptible echo or feedback response characteristics.

■    Isochronous Data Transfers:

delivery latency. (Also caRed streaming real time transfers).

A pipę supports only one of the types of transfers described above for any given device configuralion

Data Encoding/Decoding

• The USB employs NRZI data encoding when transmitting packets. In NRZI encoding. a *1" is represemed by no change in level and a ’0" is represented by a change in level.

■ The high level represents the J State on the data lines in this and subsequent tigures showing NRZI encoding. A string of zeros causes the NRZI data to loggie each bit time.

Bit Stuffing / Synchronization (SYNC)

Bit stuffing is enabled beginning with the i Ihroiighout the entire transmission. The d. Pattern is counted as the first one in a ser transmitler is always enforoed. without ex LSB First ®^yl^cPaMem , --y (Synchronization)	3ync Pattern (0x80) and ata 'one' that ends the Sync luence. BI stuffing by the , Packed Data
\ 0 0 0 0 0 0 t	.....	, , ,1^
DATA | r	6 x HIGH	Sluffed Bil
Bit Stuffed |_		^_

7