Product manual

Spinpoint M9TU-USB 3.0 Product Manual REV 1.0
56
USB INTERFACE AND USB COMMANDS
The Direction bit is set to zero to
indicate the OUT endpoint with the
specified Endpoint Number and to one
to indicate the IN endpoint. In the case
of a control pipe, the request should
have the Direction bit set to zero but
the device may accept either value of
the Direction bit.
Figure 6-32 shows the format of wIndex
when it is used to specify an interface.
■ wLength
This field specifies the length of the data transferred during the second phase of the control transfer. The
direction of data transfer (host-to-device or device-to-host) is indicated by the Direction bit of the
bmRequestType field. If this field is zero, there is no data transfer phase. On an input request, a device must
never return more data than is indicated by the wLength value; it may return less. On an output request, wLength
will always indicate the exact amount of data to be sent by the host. Device behavior is undefined if the host
should send more data than is specified in wLength.
6.3.6.3.1 Standard USB Device Request Overview
This section describes the standard device requests defined for all USB devices. Table 6-6 outlines the standard
device requests, while Table 6-7 and Table 6-8 give the standard request codes and descriptor types, respectively.
USB devices must respond to standard device requests, even if the device has not yet been assigned an address or
has not been configured.
Table 6-6: Standard Device Request
Figure 6-32 : wIndex Format when Specifying an Interface