Configurations, Interfaces, and Alternate Settings
Configurations, Interfaces, and Alternate
Settings
Device
A USB device has one or more configu-
ration. Only one configuration is active
at any time.
Config 1
High Power
Config 2
Low Power
One at a time
A configuration has one or more inter-
face, all of which are concurrently active.
Multiple interfaces allow different host-
Interface 0
CDROM
control
Interface 3
data
storage
Interface 1
audio
Interface 2
video
Concurrent
side device drivers to be associated with
different portions of a USB device.
Alt Setting
Alt Setting
Alt Setting
One at a time
0
1
3
Each interface has one or more alternate
setting. Each alternate setting has a col-
ep
ep
ep
lection of one or more endpoints.
This structure is a software model; the EZ-USB core takes no action when these settings
change. However, the 8051 must re-initialize endpoints when the host changes config-
urations or interfaces alternate settings.
As far as 8051 firmware is concerned, a configuration is simply a byte variable that indi-
cates the current setting.
The host issues a Set_Coniguration request to select a configuration, and a
Get_Configuration request to determine the current configuration.
Page 7-18
Chapter 7. EZ-USB CPU
EZ-USB TRM v1.9
CYPRESS [ CYPRESS ]
