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made using control transfers. The request and the request's parameters are sent to the device in the Setup packet.
The host is responsible for establishing the values passed in the fields listed in Table 6-5. Every Setup packet
has eight bytes.
■ bmRequestType
This bitmapped field identifies the characteristics of the specific request. In particular, this field identifies the
direction of data transfer in the second phase of the control transfer. The state of the Direction bit is ignored if the
wLength field is zero, signifying there is no Data stage.
The USB Specification defines a series of standard requests that all devices must support. These are enumerated
in Table 6-6. In addition, a device class may define additional requests. A device vendor may also define requests
supported by the device.
Requests may be directed to the device, an interface on the device, or a specific endpoint on a device. This field
also specifies the intended recipient of the request. When an interface or endpoint is specified, the wIndex field
identifies the interface or endpoint.
■ bRequest
This field specifies the particular request. The Type bits in the bmRequestType field modify the meaning of this
field. This specification defines values for the bRequest field only when the bits are reset to zero, indicating a
standard request (refer to Table 6-6).
■ wValue
The contents of this field vary according to the request. It is used to pass a parameter to the device, specific to
the request.
■ wIndex
The contents of this field vary
according to the request. It is used
to pass a parameter to the device,
specific to the request.
The wIndex field is often used in
requests to specify an endpoint or
an interface. Figure 6-31 shows
the format of wIndex when it is
used to specify an endpoint.
Spinpoint M9TU-USB 3.0 Product Manual REV 1.0
Table 6-5: Format of Setup Data
Figure 6-31 : wIndex Format when Specifying an Endpoint
USB INTERFACE AND USB COMMANDS
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