Null Transfer Function - Fujitsu F2MC-16LX Hardware Manual

16-bit microcontroller mb90330 series

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CHAPTER 13 USB FUNCTION

NULL Transfer Function

If data sent from the USB Function is the last packet and a maximum number of

packets, it is possible to automatically transfer 0-byte data in the next packet transfer.

The NULL transfer function requires that DMAE is enabled and is a function that is only

valid for IN transfer.

NULL Transfer Mode

This is the mode where if the automatic buffer transfer mode is set (DMAE=1) and IN-direction data

transfer request arrives, and a maximum number of packets are written via DMA and the last data write

decrements the number of DMA count data to "0", it automatically sets 0-byte data transfer and will send 0-

byte data for the next IN-direction data transfer request when the last IN-direction data transfer request

from the HOST has been received. The DRQ interrupt flag is not set until 0-byte data is read from the

HOST after the last data was written into a buffer via DMA. Timing by which the buffer is accessed is

shown as follows.

Only IN direction (device → host PC) forwarding

For the devices, the following processing is required:

DMAE, DRQIE, and NULE are permitting set.

Figure 13.4-13 NULL Data Transfer Operation

Data before last

DMA sending buffer

MAX packet write

Interrupt factor is