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CHAPTER 17 USB FUNCTION
17.4.1
Double Buffer
This section gives supplementary notes on the double buffer of the USB function.
■ Double Buffer
The USB function has double buffers (64 bytes × 2) for the end points for bulk transfer.
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During USB data transmission for IN transfer, the next packet data can be written by the
system to the FIFO buffer for transmission.
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During OUT transfer, the next packet can be received while data is being read from the
system.
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Buffers in the double buffer configuration are switched to each other in units of packets.
■ Timing Diagram for BULK IN Transfer (Writing by CPU and Reading by USB)
Figure 17.4-1 shows the timing diagram for double-buffer operation during BULK IN transfer and
the operation diagram.
In the example below, the MNACK bit of the CONT8 register (control register) is set so that an
IRQ signal is not asserted by NACK.
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