Table 7-14. Set Descriptor-Configuration
Byte
Field
bmRequestType
bRequest
Value
Meaning
8051 Response
Read configuration descriptor
data over OUT0BUF
0
1
2
3
0x00 OUT, Device
0x07 “Set_Descriptor”
0x00
wValueL
wValueH
0x02 Descriptor Type:
Configuration
4
5
6
7
wIndexL
wIndexH
wLengthL
wLengthH
0x00
0x00
LenL
LenH
Table 7-15. Set Descriptor-String
Byte
Field
bmRequestType
bRequest
Value
Meaning
8051 Response
Read string descriptor data over
OUT0BUF
0
1
2
3
0x00 IN, Device
0x07 “Get_Descriptor”
0x00 Config Number
wValueL
wValueH
0x03 Descriptor Type:
String
4
5
6
7
wIndexL
wIndexH
wLengthL
wLengthH
0x00 (Language ID L)
0x00 (Language ID H)
LenL
LenH
The 8051 handles Set_Descriptor requests by clearing the HSNAK bit (by writing “1” to
it), then reading descriptor data directly from the OUT0BUF buffer. The EZ-USB core
keeps track of the number of byes transferred from the host into OUT0BUF, and compares
this number with the length field in bytes 6 and 7. When the proper number of bytes has
been transferred, the EZ-USB core automatically responds to the status phase, which is the
third and final stage of the CONTROL transfer.
Note
The 8051 controls the flow of data in the Data Stage of a Control Transfer. After the
8051 processes each OUT packet, it loads any value into the OUT endpoint’s byte count
register to re-arm the endpoint.
EZ-USB TRM v1.9
Chapter 7. EZ-USB CPU
Page 7-17
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