Canon CANOSCAN D660U Service Manual page 40

CHAPTER 2
USB cable has A plug for connecting to upper layer and B plug for connecting to lower layer.
3. USB data transfer
USB data is transferred in the following four data structures called "packet".
* Token packet
* Handshake packet
* Data packet
* Special packet
USB device may support multiple data transfer endpoints, so there are four types of data
transfer protocols.
* Isochronous transfer : Allocates a data transfer time to a device. Highest priority is given but
* Interrupt transfer
* Control transfer
* Bulk transfer
2 - 20
A Plug
Figure 2-21
: Used to start a data transfer
: Used to report the status of a data transfer
: Used to send and receive data
: Used for other transfer
no error is corrected.
: Periodically transfers data within a specified waiting time. Second
priority is given.
: Used to configure the host computer when USB device is attached/
removed.
: Lowest priority is given but larger amounts of data is sequentially
transferred to a free bus.
COPYRIGHT © 2000 CANON INC.
B Plug
CANOSCAN D660U REV.0 JULY 2000 PRINTED IN JAPAN (IMPRIME AU JAPON)