189
Chapter 7
DMA Functions (DMA Controller)
Preliminary User’s Manual U15839EE1V0UM00
7.5.2 Single-step transfer mode
In single-step transfer mode, the DMAC releases the bus at each byte/halfword/word transfer. Once a
DMA transfer request signal is received, transfer is performed again. 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.
Figure 7-20, “Single-Step Transfer Example 1,” on page 189 shows a DMA transfer example in single-
step transfer mode.
Figure 7-20:
Single-Step Transfer Example 1
Figure 7-21, “Single-Step Transfer Example 2,” on page 189 shows a DMA transfer example in single-
step transfer mode in which a higher priority DMA transfer request is generated while the lower DMA
channel has released the bus.
Figure 7-21:
Single-Step Transfer Example 2
Note: The bus is always released
DMA1
CPU
CPU
CPU
CPU
CPU
CPU
CPU
CPU
DMA1 CPU
CPU
DMA1
DMA1 CPU
CPU
CPU
Note
Note
Note
DMA Transfer
Request CH1
DMA channel 1
terminal count
DMA0
DMA0
CPU
CPU
DMA1 CPU
CPU
CPU
CPU
DMA1 CPU
CPU
DMA1
DMA0 CPU
DMA1 CPU
Note
Note
Note
Note
Note
Note
DMA Transfer
Request CH0
DMA Transfer
Request CH1
DMA channel 0
terminal count
DMA channel 1
terminal count
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