CHAPTER 12 USB FUNCTION CONTROLLER (USBF)
Preliminary User’s Manual U19014EJ1V0UD
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(9) UF0 descriptor length register (UF0DSCL)
This register stores the length of the value that is to be returned in response to the GET_DESCRIPTOR
Configuration request. The value of this register is the number of bytes of all the descriptors set by the
UF0CIEn register minus 1 (n = 0 to 255). The total descriptor length that is to be returned in response to the
GET_DESCRIPTOR Configuration request is determined according to the value of this register.
This register can be read or written in 8-bit units. However, data can be written to this register only when the
EP0NKA bit is set to 1.
Processing of wLength is automatically controlled. If this register is set to 00H, it means that the descriptor to
be returned is 1 byte long. If the register is set to FFH, a descriptor length of 256 bytes is returned. When a
descriptor exceeding 256 bytes in length is used, set the CDCGDST bit of the UF0MODC register to 1 and
process the GET_DESCRIPTOR request by FW (at this time, the CDCGD bit of the UF0MODS register is also
set to 1).
Caution To rewrite this register, set the EP0NKA bit to 1 before reading the register contents, and
rewrite the register contents after confirming that the bit has been set, in order to prevent
conflict between a read access and a write access.
DPL7
UF0DSCL
DPL6
5
DPL5
DPL4
3
DPL3
2
DPL2
1
DPL1
DPL0
Address
FF78H
After reset
00H
0
4
6
7
Bit position
Bit name
Function
7 to 0
DPL7 to
DPL0
These bits set the value of the number of bytes of all the descriptors to be returned in
response to the GET_DESCRIPTOR Configuration request minus 1.
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