Chapter 4 Software Development
page 4-6
4-1-8. Data Rates
The USB supports two data rates: 12 Mb/s and 1.5 Mb/s. Table 4.1.4 lists the maximum payload
sizes for each combination of data flow type and data rate.
Table 4.1.4. Maximum Payload Sizes
MAX Payload Size
Transfer Types 12 Mbps 1.5 Mbps
Control 8/16/32/64 8
Isochronous 1023 or less N/A
Interrupt 64 or less 8 or less
Bulk 8/16/32/64 N/A
A hub determines the data rates supported by an attached function by examining the latter's Non
Return to Zero Invert (NRZI) data signal lines (D+ and D-). A device supporting the high speed
pulls up the D+ line to the 3.3-volt power supply voltage with a 1.5-kΩ resistor; one supporting the
low speed does the same with the D- line.
The ML60851C USB controller operates exclusively at 12 Mb/s, so the JOB60851 board includes
only the D+ pull-up resistor.
4-1-9. Device Class Specifications
The Universal Serial Bus Device Class Specifications complement the core specifications by further
standardizing USB devices for major interfaces and specific applications devices using those
interfaces.
Some interface specifications standardize the communications pathways that the USB hardware
provides for a specific purpose--the exchange of isochronous audio or image data, for example.
Others standardize USB specifications for devices combining multiple interfaces.
Table 4.1.5 lists some of the USB Device Class Specifications currently available. For further details,
refer to the following URL.
Table 4.1.5. USB Device Class Specifications
Device Class Applicable Equipment
Human interface devices (HIDs) Mice, keyboards, joysticks, etc.
Printers Printers
Audio devices Speakers, microphones, etc.
Communications devices Modems, ISDN terminal adapters, etc.
Mass storage devices Fl oppy disk drives, SCSI equipment, ATAPI equipment, etc.
Image devices Digital cameras, scanners, low-rate video, etc.
There is also a standard for downloading programs to devices.
http://www.usb.org/developers/devclass.html