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CHAPTER 16 DMA CONTROLLER (DMAC)
■ Demand Transfer
Figure 16.4-3 shows the operation flowchart for demand transfer.
DENB=>0
Reload enable
Demand transfer
- Only requests from the external pin (DREQ) are accepted. Activation by
other sources is disabled.
- Access to an external area is required (since access to an external area
becomes the next activation source).
- The number of blocks is always 1, regardless of the settings.
- Interrupt clear and the DMA interrupt are issued when transfer for the
number of times specified is completed.
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Figure 16.4-3 Operation Flowchart for Demand Transfer
DMA stop
DENB=1
None
Activation request
wait
Activation request
Load the initial address,
transfer count, and
number of blocks
Calculate the address for
transfer source address access
Calculate the address for transfer
destination address access
Number of blocks - 1
Write back the address,
transfer count, and number
of blocks
DTC=0
Interrupt clear
DMA transfer end
One-time access for fly-by
Only when the peripheral interrupt
activation source is selected
Interrupt cleared
DMA interrupted
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