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Section 22 USB Function Module (USB)
22.8.3
DTC Transfer for Endpoint 2
When the transmit data at EP2 is transferred by the DTC, the USB function module automatically
performs the same processing as writing 1 to the PKTE bit in TRG if the currently selected FIFO
(64 bytes) becomes full. Accordingly, to transfer data of a multiple of 64 bytes, the user need not
write 1 to the PKTE bit. To transfer data of less than 64 bytes, the user must write 1 to the PKTE
bit on a DTC transfer end interrupt. If the user writes 1 to the PKTE bit when the maximum
number of bytes (64 bytes) are transferred, correct operation cannot be guaranteed.
To end the DTC transfer, write 0 to the EP2EMPTY bit in IFR0, after clearing the EP2DMAE bit
in DMA to 0 within the processing routine for a DTC transfer end interrupt. If this procedure is
omitted, the DTC transfer end interrupt is not cleared. To perform the DTC transfer again, in
addition to the said procedure, set the number of transfers, set the DTCERF register, and then set
the EP2DMAE bit in DMA to 1.
Figure 22.21 shows an example for transmitting 150 bytes of data to the host. In this case, internal
processing which is the same as writing 1 to the PKTE bit in TRG is automatically performed
twice. This internal processing is performed when the currently selected data FIFO becomes full.
Accordingly, this processing is automatically performed only when 64-byte data is sent.
When the last 22 bytes are sent, the internal processing for writing 1 to the PKTE bit is not
performed, and the user must write 1 to the PKTE bit by software. In this case, the application has
no more data to transfer but the USB function module continues to output DTC requests for EP2
as long as the FIFO has an empty space. Therefore, when all data has been transferred, write 0 to
the EP2DMAE bit in DMA to cancel DTC transfer requests, and then write 0 to the EP2EMPTY
bit in IFR0 to clear the request for a DTC transfer end interrupt.
Rev. 1.00 Mar. 12, 2008 Page 888 of 1178
REJ09B0403-0100
64 bytes
PKTE
(Automatically
performed)
Figure 22.21 PKTE Bit Operation for EP2
64 bytes
22 bytes
PKTE
(Automatically
performed)
Execute by DMA transfer
end interrupt (user)
PKTE is
not performed
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