187
Chapter 7
DMA Functions (DMA Controller)
Preliminary User’s Manual U15839EE1V0UM00
7.5 Transfer
Mode
7.5.1 Single
transfer
mode
In single transfer mode, the DMAC releases the bus at each byte/halfword/word transfer. If there is a
subsequent DMA transfer request, transfer is performed again once. This operation continues until a
terminal count occurs.
When the DMAC has released the bus, if another higher priority DMA transfer request is issued, the
higher priority DMA request always takes precedence. However, if a lower priority DMA transfer request
is generated within one clock after the end of a single transfer, even if the previous higher priority DMA
transfer request signal stays active, this request is not prioritized and the next DMA transfer after the
bus is released for the CPU is a transfer based on the newly generated, lower priority DMA transfer
request.
Figure 7-16, “Single Transfer Example 1,” on page 187 shows a DMAC transfer in single transfer mode.
In this example the DMA channel 3 is used for a single transfer.
Figure 7-16:
Single Transfer Example 1
Figure 7-17, “Single Transfer Example 2,” on page 187 shows DMAC transfers in single transfer mode
in which a higher priority DMA transfer request is generated. DMA channels 0 to 2 are used for a block
transfer and channel 3 is used for a single transfer.
Figure 7-17:
Single Transfer Example 2
Note: The bus is always released
CPU
DMA3
CPU
CPU
DMA3
CPU
CPU
CPU
CPU
CPU
DMA3
CPU
DMA3
DMA3
CPU
CPU
CPU
CPU
CPU
DMA chan nel 3 terminal count
Note
Note
Note
Note
DMA Transfer
Request CH3
DMA Transfer
Request CH0
DMA1
DMA2
CPU
DMA2
CPU DMA3
CPU
CPU
CPU
DMA3
CPU
DMA0
DMA0
CPU
DMA1
CPU DMA3
Note
Note
Note
Note
DMA Transfer
Request CH1
DMA Transfer
Request CH2
DMA Transfer
Request CH3
DMA channel 0
terminal count
DMA channel 1
terminal count
DMA channel 2
terminal count
DMA channel 3
terminal count
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