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Chapter 15
DMA Functions (DMA Controller)
User’s Manual U16702EE3V2UD00
15.5 Transfer
Modes
In the following examples it is assumed that TCS is set as “1” for all DMA channels.
15.5.1 Single
transfer
mode
In Single transfer mode, the DMA releases the bus after each transfer. If there is a subsequent DMA
transfer request, the transfer is performed again when the bus becomes available again. This operation
continues until the transfer counter is cleared to 0 and the internal TC signal is generated.
When the DMA has released the bus, if another higher priority DMA transfer request is issued, the
higher priority DMA request always takes precedence.
A Single transfer mode example is shown in Figures 15-13 and 15-14.
Figure 15-13 shows the transfers of DMA0 with DMBC0 set to 3 at the beginning of the transfers:
Figure 15-13:
Single Transfer Mode Example (1 Channel)
Figure 15-14 shows the Single Transfer mode with DMA requests on multiple DMA channels. The
number of transfers is set to 2 for all channels (DMBCn=1) at the beginning.
Figure 15-14:
Single Transfer Mode Example (3 Channels)
After each bus release, the DMA controller checks which pending DMA request has the highest priority,
delaying the execution of the lower-prioritized DMA transfer accordingly.
CPU
CPU
CPU
CPU
CPU
CPU
CPU
DMA0
CPU
DMA0
CPU
DMA0
CPU
DMA0
CPU
DMMRQ0
INTDMA0
Note
Note
Note
Note
Note:
The
bus
i
s
a
lw
a
y
s
rele
as
ed.
CPU
CPU
DMA4
DMA4
CPU
CPU
CPU
CPU
DMA0
CPU
DMA2
CPU
DMA0
CPU
DMA2
CPU
DMMRQ4
INTDMA0
<1>
<1>
<2>
<2>
<
3
>
<
3
>
<4>
<4>
<5>
<5>
<6>
<6>
Note
DMMRQ2
DMMRQ0
Note
Note
Note
Note
INTDMA2
INTDMA4
Note:
The
bus
i
s
a
lw
a
y
s
rele
as
ed.
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