UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
225 of 362
NXP Semiconductors
UM10208
Chapter 17: LPC2800 USB Device
8.19 USB Data Count Register (USBDCnt - 0x8004 101C)
Table 249. USB Data Count Register (USBDCnt - 0x8004 101C)
Bit
Symbol
Description
Master
Reset
value
Bus
Reset
value
10:0
For an IN (TX) endpoint, write the USBEIX register to select
it, then write this field with the number of bytes in the next
packet to be sent by the endpoint. Then write that many bytes
to the Data Port Register, or let a DMA channel transfer that
many bytes from ARM memory to the endpoint’s TX buffer.
When the number of bytes indicated by the register have
been written, the TX buffer is marked “valid”. The packet will
be sent in response to a future IN token for the endpoint. The
value written to this field may not be larger than the Max
Packet Size for the endpoint. Writing zero to this field results
in the transmission of one empty packet. This field is
automatically loaded with the value in the endpoint’s Max
Packet Size Register when the host ACKs the IN packet.
For an OUT (RX) endpoint, the hardware loads this field with
the number of received bytes when the USB controller ACKs
an OUT packet from the host. Write the USBEIX register to
select the endpoint, then read this field to determine the
number of bytes in the buffer, then read that many bytes from
the Data Port register, or let a DMA channel transfer them
into ARM memory. When the number of bytes indicated in
this register have been read, the buffer is automatically
cleared and made ready for the next data packet.
0
0
31:11 -
Reserved, software should not write ones to reserved bits.
The values read from reserved bits is not defined.
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