Silicon Laboratories Stepper Machine Specifications download pdf (Page 34)

Standard Requests Values

 These tables indicate the bRequest values and the wValue values defined by the USB spec

 From the previous slide it can be seen that the wValue field can take on several different meanings

based on the request

11SET_INTERFACE

12SYNCH_FRAME

10GET_INTERFACE

9SET_CONFIGURATION

8GET_CONFIGURATION

7SET_DESCRIPTOR

6GET_DESCRIPTOR

5SET_ADDRESS

4Reserved for future use

3SET_FEATURE

2Reserved for future use

1CLEAR_FEATURE

0GET_STATUS

ValueStandard Request

8INTERFACE_POWER

7OTHER_SPEED_CONFIGURATION

6DEVICE_QUALIFIER

5ENDPOINT

4INTERFACE

3STRING

2CONFIGURATION

1DEVICE

ValueDescriptor Type

bRequest Field: What request? wValue Field: Get_Descriptor Request

2DeviceTEST_MODE

0EndpointENDPOINT_HALT

1DeviceDEVICE_REMOTE_WAKEUP

ValueRecipientFeature Selector

wValue Field: Set_Feature Request

Let’s take a look at some of the values that are defined. Above we see the different

values associated with the fields that were in the table on the previous slide. These

are the values that get populated in the data for the setup phase of the standard

request (the 8 data bytes). For example, if the second byte (bRequest) is 0x06 the

host is requesting a descriptor or if it is a 0x05 the host is going to set our address.

The wValue field shown above goes deeper into the request. If we receive a 0x06

and have determined that the host is asking for a descriptor the wValue field will

tell us which descriptor the host is asking for. For example, if wValue is set to 0x01

then the host wants our device descriptor. As firmware developers we need to be

able to parse through the data received and take appropriate action.

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