Canon CANOSCAN N1220U Service Manual page 42

CHAPTER 2
USB connector has A plug for connecting to upper stream and B plug for connecting to
lower stream.
3. USB Data Transfer
USB data is transferred in the following four data structures called "packet".
1) Token packet
2) Handshake packet
3) Data packet
4) Special packet
USB device may support multiple data transfer endpoints, so there are four types of data
transfer protocols.
1) Isochronous transfer : Allocates a data transfer time to a device. Highest priority is give
2) Interrupt transfer
3) Control transfer
4) Bulk transfer
This scanner uses control transfer and bulk transfer.
2 - 22
COPYRIGHT 2000 CANON INC.
A Plug
Figure 2-23
: 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
but any error is not 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.
CANOSCAN N650U/N656U/N1220U REV.0 JUNE 2000 PRINTED IN JAPAN (IMPRIME AU JAPON)
B Plug