UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
226 of 362
NXP Semiconductors
UM10208
Chapter 17: LPC2800 USB Device
8.20 USB Data Port Register (USBData - 0x8004 1020)
8.21 USB Short Packet Register (USBShort - 0x8004 1024)
This read-only register indicates whether the most recent packet received by each of the
various OUT (RX) endpoints had a packet length less than the value in the endpoint’s Max
Packet Size Register.
Table 250. USB Data Port Register (USBData - 0x8004 1020)
Bit
Symbol
Description
Master
Reset
value
Bus
Reset
value
31:0
This register is not used for an endpoint that uses a DMA
channel.
For an IN (TX) endpoint that doesn’t use a DMA channel,
write the USBEIX register to select it, then write the Data
Count Register with the number of bytes in the next packet to
be sent by the endpoint. Then write that many bytes to this
register. Each write except the last is considered to contain 4
bytes. The last write is considered to contain 4 bytes if the 2
low-order bits of the Data Count Register are 00, otherwise it
is considered to contain the number of bytes in those 2
LSbits, in the LSbytes of the value written. Software may
have to shift the data to accommodate this convention.
For an OUT (RX) endpoint that doesn’t use a DMA channel,
write the USBEIX register to select the endpoint, then read
the Data Count Register to determine the number of bytes in
the buffer, then read that many bytes from this register. The
hardware provides four bytes for every read except the last. If
the 2 low-order bits of the Data Count Register are 00, that
read provides 4 bytes, otherwise the it provides the number
of bytes indicated in those 2 LSbits, in the LS bytes of the
word. Software may have to shift these bytes to
accommodate the buffering conventions of the application.
Remark:
The Last Valid Byte is kept on the LSB side.
0
0
Table 251. USB Short Packet Register (USBShort - 0x8004 1024)
Bit
Symbol
Description
Master
Reset
value
Bus
Reset
value
7:0
OUTSH
1s in these bits indicate that the most recently received OUT
packet on that endpoint was shorter than the endpoint’s Max
Packet Size. Bit 0 indicates this for logical Endpoint 0; bit 7
for logical Endpoint 7.
0
0
31:8
-
Reserved. The values read from reserved bits is not defined. -
-